1996 GTS High Idle (2500-3500) at high altitude (8000-9000 ft)

I've had this happen twice. At high altitude in the Sierra Mountains in NV/CA, engine idle will increase to 2500 (and as high as 3500) in a few seconds. Dwell there for 5 to 20 seconds and then "burp" or "fart" down to proper idle. At normal altitude of 4000-5000 when I would back off going down a hill, there would be a slight delay in rpm drop and then the car would "burp" out the exhaust and drop to idle. Most cars will not drop to idle the instant the throttle drops to closed.

Mods are cam, heads, headers, no cats, VEC1.

Today I was on the Quincy La Porte Road and was fighting this 3500 rpm idle descending 15 mph wet and muddy hair pins over 8000 ft. It was pretty much the direct opposite of fun.

I was able to stabilize the idle around 1800 by setting the VEC1 Low to MIN setting (!) The idle would hunt but now the range was maybe 100 rpm at most.

What is interesting is that this ONLY happens when over 8000 ft. and it does not always happen. There is an 8900 ft summit I drive fairly regularly but I'm not above 8000 very long and also driving at a good rate of speed - no low mph or engine braking. The other time car did this was over CA Route 4 which turns into a 12 ft wide "driveway" with sheer drop offs and blind hair pins. Again very slow and lots of engine braking.

I'm thinking

• MAP
• IAC
• VEC1

I'm thinking the IAC has to be opening. Then the question is WHY?
I'm also thinking NOT vacuum leak.
Also, the "exhaust fart" when backing off - especially downhill. Is that normal? (I can't remember if my stock 2000 did that.)

Any help would be greatly appreciated.

I'd like to drive this car to 14,000 ft in the Rockies and don't want the idle going to 5500 rpm (!!!!)

Thanks
Tom

Is your computer stock or modified?

Don't know. It had California Official Upgrades done to it - there are official tags in the engine compartment.

My guess is no. TNT Motorsports did the heads and cam and then a 150 shot nitrous system was added - I would have to guess that someone local in SoCal did that. NOTE: The nitrous steals fuel from the injector rails (rhs aft port on manifold.

I just had it near 7000 ft (Lake Tahoe) and while not a problem, it did it classic behavior: Backed off using engine braking down off the summits, you take your foot off throttle, then 1-2 seconds later, the IAC closes (assuming - lets say the throttle blades close) and with that there is a loud crackle and then rumblings out the tailpipe. It has always done that for the past 10k miles (has 81k on it) and I never paid it much attention. Perhaps that is improper operation?

At 9000 ft (roughly 3000 meters) atmospheric pressure is about 70% of sea level. So figure about 10 psi atmospheric.

Does the 1996 GTS computer (same as Mopar Race Computer, right?) have a BARO input or is it part of the MAP?

What would happen if its getting "BARO" wrong? If it thought BARO was Sea Level, then 10 psi would be part throttle which it seems like its doing.

Of course the ECU takes all the info and decides IAC input (I'm guessing its the IAC that is operating incorrectly - how could you get a 3500 rpm idle w/o IAC opening?)

MORE INFO:

Turns out it is going on at 4500 altitude - never really noticed it because at this altitude, the idle sometimes hangs around 1500-1700.

The VEC1 LOW can act as an idle speed control - but its not that simple.

At this altitude, adjusting LOW to MAX or MIN causes it to drop to idle.

When at idle, LOW has no effect on idle rpm (full LOW causes engine to basically flame out and stop running.)

However, if the throttle is pressed, the high idle will return. (and then the VEC1 LOW can cause it to drop to normal idle.)

I hooked a scan tool and got codes P1489 Hi Spd Fan CTRL Relay Circ and P0175 2/1 Fuel System Rich.

Read at IDLE:

• MAP = 5.9 in-Hg and was changeable by VEC1 LOW
• Ignition Advance = 15 deg but also would show up 4 deg. Not obviously changed by VEC1 LOW

I'm trying to remember something about swapping Viper relays if .... ??? Might have actually done this in my 2000 at a Viper Days but I simply do not remember. Maybe I pulled a fan relay??? Better go check...

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EDIT: Two more things:

• VEC1: any easy way to disable?
• MAP: any easy way to disable and force ECU into Speed Density Mode? (Chevy guys can do this)

And also: wonder if pulling connecter off IAC might be a way to deal with high altitude idle runaway?

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EDIT NUMBER 2:

If 6 in-Hg is a vacuum leak AND one bank is running rich, THEN there is a vacuum leak on the other bank???

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EDIT NUMBER 3:

TEST MAP reading -v- vacuum gauge
This should allow confirmation of MAP output and VEC1 operation.

This issue is very common on head and cam change cars when the tuning is not precise. There is an area in the Map where the computer does not understand the relation between MAP and TPS, the high idle is mostly timing advance, not IAC motor steps. The computer reads Barometric pressure through the MAP sensor at key on, so if the tuning is a little off at sea level it might be way off at 4500 feet.

Hope this helps, get it back on a good load dyno and have it tuned under various loads and rpm points.

Thanks Dan!

So it you start the engine at 5000' and then drive to 9000' , the ECU think BARO is still at 5000?

I seem to recall when it did this 10k miles ago, I tried shutting engine off and then starting. This last episode I didn't try that.
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The idle being timing and not IAC is interesting. Just testing idle to get the codes, I adjusted VEC1 LOW and saw MAP change up and down as expected AND timing seemed to be either 4ish or 15ish ADV.

The not the cheapest scan tool that I was using allowed monitoring maybe 15 streams one of which was ADV. It would be interesting to keep the scan tool up and running every time I drive the car to see what might be going on. I would have MAP and ADV available. But I guess there is no way to see what BARO is (if that is the proper name for Chrysler.)
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That P0175 only is bugging me too...
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I was in NV for a couple weeks and am now leaving Tuesday. My next trip is to pick this Viper up and drive it back to the other side of Pittsburgh PA. I've put about 10k on it in this condition and don't seem to see any adverse effects - probably not a big deal because I have never been interested in top end shots. Too Old, Too Paranoid, Too Broke. Back in PA I have to build a Supercharged Studebaker R2 for a guy I sold engine to AND finish this crazy tar baby 1974 Datsun pickup I couldn't resist buying - need some kind of support group can call 24/7 if get the urge - especially if a Jag.

Thanks all,
Tom

Just had a theory on what could be happening taking into consideration the P0175 rich bank code.

It actually goes back to the dyno curve on nitrous.

This car had 123 bottles through the 150 shot system. The fuel system was left stock and fuel to the nitrous nozzles was taken from the injector rail.

The dyno chart is strong up to 4000 rpm when dramatically over the next 500 rpm, 80 HP is lost. Then the HP declines at a fairly steep slope. I was at PRI and talked to a guy from NX (I think that is the brand system) and said instantly that I had a bad solenoid valve - something about the seat was damaged. He said send it in for a free replacement - I guess they have a lifetime warranty.

One bank running rich.

High idle.

What if I have leaky fuel solenoid?

I'm guessing there is one solenoid but there are 2 spray nozzles. I don't know how they are plumbed, but it might be possilble that one bank sees leaking fuel past the solenoid.

Also, seems like mileage is way off on the car. Getting just over 200 miles to a tank when previously I would get 300. Don't think the VEC1 could be responsible for that.

Does the 1996 OBDII have short and long term fuel trim codes? ...just wondering how I could get a bank running rich code and not have a trim code.

Still could be a vacuum leak. 123 bottles presents a lot of opportunity for a good backfire through the intake.

Dan, You said something that I found quite troubling:


Is this related to LOAD calculation which might cause some circular dependencies?

MAP based fuel injection systems use manifold vacuum and throttle position as its major factors to determine fuel and timing maps. Bigger cams lower engine vacuum at low speeds and take quite a bit of tuning to get right. If engine vacuum and throttle position readings do not corrospond correctly, then issues with high idle and driveability can result. MAP based Vipers require proper tuning with big cams, sometimes you need to make changes before you get it just right.

Flying back to NV and this problem Friday (+4 days from now)

I have to decide whether to try and fix this while I have access to high altitude before I take the car back to PA.

The one thing that I suspect is a simple intake manifold leak. Perhaps it would be worth to simply replace them.

The other thing is getting it fixed by a Tuner while on the West Coast - there are way more there. Cragin would be a strong choice but he is 7.5 hours away in LA - I'm 3 hours from Bay Area.

I don't know if there are any shops near Pittsburgh that would do a good job - and once I get it back to PA, the highest altitude nearby is 5000' in West Virginia. So there wouldn't be any meaningful road test to "certify" the car for 14,000' in the Rockies if I ever take it there.


Previously, I was planning to drive the car cross-country and stop off at points of interest like the Rockies and Pikes Peak, but this year has been one of one disaster after another - so my ability to tolerate further hassles is fully depleted.

Still, I might drive it back.

If you're trying to solve a tricky condition like this. I would think the 7.5hrs drive to Dan would be your best bet. At least your car would be fix the first time around and done right.

I still haven't talked to Dan yet (left message) and from what people say, he is The Guy. I wish there was someone closer. Ted May @ Valaya is 3 hours away from Carson City, NV and I don't know what is available near Pittsburgh.

My concern could be trivial or a complete mess.

One question is what might TNT Motorsports have done regarding programming? This was a 1996 GTS that was modded shortly after purchase. Maybe they didn't mod the ECU at all in which case, some kind of add-on might be a better way to go? What are the sensible options? (I'm a computer programmer and have tuned muscle cars and would have no hesitation at all learning to tune an LS1. But it has tons and tons of support. Tuning Viper sounds like an elite fraternity.)
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MORE DIAGNOSTIC THOUGHTS:

P0175 Bank 2 Fuel System Rich Code is the only code (except for a High Fan P1489).

Supposedly this code trips when the LT trim is maxed out. (so why no LT trim code???)

The VEC 1 is a MAP translator. And since the issue is dramatically related to altitude (BARO), anything "pressure" I suspect. I have read in general BARO is part of OBDII MAF sensor, but I think Viper sets BARO from MAP when engine starts - I could be completely wrong on this one.)

So a flakey VEC 1 is a possibility - and I think it still has the piercing connectors which I know for a fact, fail - I calibrate taxi meters and those VSS connections get noisy over time and the meter fails due to bad input. They must be soldered or at least crimped. I can't remember if I soldered them, but I'm thinking not.)

Good Grief! this thing is Speed Density!

Argh........ (unavailable Banging Head Against Brick Wall emoticon)
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EDIT:

Plan of action: first fix the P0175 Bank 2 rich AND 33% loss in fuel economy (200 miles per tank instead of 300).

First scan and see what is going on with fuel trims and O2 sensor. (bot a DRBIII 12 years ago - time to use)

Guesses:

• Injector fuel plenum leak. (QUESTION: I'm guessing the remedy is new injector o-rings?)
• Intake vacuum leaks- hopefully find someone locally (Carson City, NV) to smoke it.

THEN see what's going on with this idle hang.

UPDATE:

Back in NV and had the 3000 rpm idle hang at a mere 6200 ft.

However, now with two "recent" events, I believe it is a "cold" temperature event. These past two events occurred with ambient temp in the 50's which is unusally cold in NV when I visit.

Fuel economy is now about 150 miles per tank which is about 1/2 of what I usually get.

My current theory is that I've got injector seal leaks in Bank 2 (P0175).

Also, when I restart after a trip to a store, etc. the engine runs up like my foot is on the gas. This subsides immediately. As if I shot starting ether in the intake. So I strongly suspect the injector seal leak.

I am going to focus on this leak issue and see what has been talked about on the internet.

If I dont find specifics I'm looking for, I'll probably start a thread on this failure mode - the obvious QUESTION: What symptoms occurred when this failure occurred? (With a Bank 2 Rich, there MUST be a failure either in measurement or fueling.)

UPDATE: 9/3/2015:

VEC1 MAP intercept wiring was *****!

Installation consists of cutting the MAP wire at the ECU harness, crimp blade terminals onto the ends, and then connect with terminals from the VEC1.

The crimp terminal coming off the ridiculously short cut they decided to make at the ECU harness connector FELL OFF!

1/2 the wires were completely gone due to oxidation (!) within the crimp.

So I've soldered ALL connections at the ECU: MAP in and out and the pair of wires for the O2 sensor.

Since the VEC1 has always had a big effect dealing with the crazy high idle, I've always suspected the wiring and only now have corrected it. I am not going to get up into the dash because, hopefully, the environment there will be benign enough to not oxidize the connections. Those connections are the 12v and the dimmer that runs off the headlight circuit.

Recent driving has clearly indicated it is not related to altitude (did the 3000 rpm hang at 6000' where I had parked for dinner - car was fine driving there (and all over the place at that altitude) but when I start it up to drive home, within a minute it was all wonky with the 3000 nonsense again.

The next day at home, that all went away.

These events seem more related to a chilly night temperature which could explain it: thermal expansion might be just enough to mess with the oxide layer to change conductivity.

I'll be buttoning it up shortly and off to the Virginia City "Hill" and points unknown!

UPDATE: 9/6: With soldered VEC1, engine has been very stable and more HP - can now churn the tires in 1st.

No incidents until just now - I took car to 6200 ' AND a little chilly 55*F (maybe even a few more degrees cooler), and the idle hanged around 1300-1500 rpm.

Knowing that the VEC1 Low adjusted richer will drop a hang, I gave it 2 clicks to a final position of 4 and the idle dropped.

This is the first hang since I soldered the VEC1 connections and I don't think I've had it in that cold a day at that altitude. (although it is still possible.)

The VEC1 is now set at 4 on both Low and High adjusters.

Perhaps a combination of altitude and temp (i.e. density) poses a problem for the ECU programming. And perhaps the VEC1 can be used to tweak the MAP signal for these variations.

All I can do for now is continue to drive the car at all different combinations.

Tomorrow early in the AM, the temperature will be 30, so I think I will be up at the break of dawn and get to some altitude and see what happens. (looks like it is going to 8911 feet at Mt. Rose Summit)

UPDATE: 9/10:

Took to Mt. Rose 8900' 30*F and got a minor 1400 rpm idle hangafter shutting off at summit, then starting after about a 10 min "heatsoak."

The hang occurred right after the cold start enrichment was over.

One VEC1 click rich caused the hang to drop. (One click back cause the hang to reappear.)

What is interesting is if I set the VEC1 Low leaner and leaner, I can produce a higher and higher idle hang. The difference this time is that this behavior is stable and precise. With the loose connector(s), results from adjusting VEC1 were very erratic.

QUESTION: I wonder if a high idle hang occurs when anyone sets the VEC1 Low leaner???

For now, I'm going to consider this case closed. I have a workaround for idle hangs. I don't know if my ECU has been programmed (I suspect not because of CA emissions inspections) or if it should be tuned - I don't know what the advantages of a tune would be.

Frankly, if there are issues driving a Gen 2 at various altitudes with the Ken On BARO no matter what the programming, perhaps the VEC1 is a solution given the ECU limitations (if they exist.)
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REGARDING DTC's and FUEL ECONOMY:

Touring around, I've gotten 300 miles out of a tank, so that is now where it should be.

The P0175 Bank 2 Rich is now gone leaving the P0158 Bank 2 sensor 2 O2 Sensor Circuit Shorted to High which I believe is typical for a headers and "full exhaust." I don't have the Bank 1 code so I suspect there is a problem with the "handling" of the Bank 2 rear O2 sensor. QUESTION: if I need a new "sim" Type to get?

The P1489 Hi Speed Fan Control Relay Circuit shows because I have the "yellow" relay installed with is a hard wired High make.

Regarding the CEL:

• It would be nice to not have it, but with the yellow relay, I believe that is unavoidable unless I can change something with my DRBIII - would like advice on this.
• If I need to clean the CEL for PA emissions inspections (when I bring back from NV), I'll have to fix the P0158 - I can clear the P1489 by installing the proper Fan Speed relay.

UPDATE: DRBIII IAC WIGGLE TEST:

Did this and the engine would jump from 1300 to 1900 every time the IAC was ramped open. Closing was fairly smooth. (No way to plot this information on DRB which really defeats the whole purpose of the test: inspection of the curve.)

I suspect this could be related to the idle hang issue.

Just saw on Roe's site that when you ask for a tune, you specify altitude. 0-2k, 2k-5k, etc.

You can't even "recal" with am Engine-Off/Key On if you drive from 4k-9k in a half hour.

I drive from 0-9k altitude and was planning on trip to Pike's Peak and Rocky Mountain play where you get to 14k.

Although I would never consider it, I wonder what the AEM 30-1500 Series 1 did with BARO...

An UPDATE and a couple QUESTIONS...

UPDATE:


What to do.... I guess try DRBIII on another car????

WHAT IS BARO USED FOR?:

BARO is probably used to establish backpressure since manifold pressure needs no further characterization. The table is linear and consists of two points - so I'm been told. It is typically disabled for boosted cars which I don't understand.

DRB III should work using SuperCard 2