High speed surging

[Bonkers]

I've spent the past couple of hours looking into this, but I see a lot of diagnois and no cures. My car has an annoying, almost pulsating, surge-thing going on at highway speeds now. It was more noticable on my way home from VIR, but I just took it as a combo of my heat sickness and 7hr drive. Tonight I noticed the car didn't start as quickly as it used to. The search button yeilded two results - idle hang and/or TB failure.

My first question - could this be simply a symtom of the stock TBs choking the rest of the free-flowing air/exhaust system? If not, what causes a TB to "fail?" Is there a simple solution to fixing this problem?

Now the real prize in this crackerjack box is whether or not the car has always done this. I have really low HP numbers and the car may never have had the grunt to do this at speed before. Its really annoying so any quick advice on how to correct would greatly be appreciated.

 

[Joseph Dell]

70mm throttle bodies are notorious for this. Also, a sticky idle air motor can cause this as well. replacing the idle air motor may be a fix or simply removing it and cleaning it.

on the older cars, idle hang was from the throttle plates being out of sync. but gen II's don't have that issue.

my car only started doing it w/ 70mm TB's and the idle air motor being replaced helped fix it a bit. for my car, it tended to happen more when the motor was cold (cold start, that is... not cold weather although it did it in cold weather too).

or it could be a basic vaccume leak. check for that too. i don't recall what your combo is but something as simple as a vaccume leak or an exhause leak (header) will cause the A/F mixture to be off and the car to try to compensate.

good luck!

 

[Randy]

on the older cars, idle hang was from the throttle plates being out of sync. but gen II's don't have that issue.

Actually (as I'm sure you know better than I), Gen II's have the same issue as the Gen I's with off-idle surging, its just a lot harder to get the Gen II's out of sync (since the Gen I's dual cable and easily changed cable adjustment were notorious for one cable moving when you go to wide-open-throttle, until you put the screw in the adjustment plate). I've had to adjust my Gen II's between-throttle-body linkage once when it started bucking at low speed.

However, I don't believe the off-idle surging/bucking really manifested itself at higher speeds.

 

[V10SpeedLuvr]

Bonk, try my fix (well, Tom Sessions fix) of regrounding the TPS at the PCM and the sensor. My car mostly surged in low speeds, but also did the same thing at high speeds (50-60mph) a few times as well