Im having a surging issue on my 92 rs, its a 305 TPI from an 86 formula, it has been converted to Speed Density, I have had so many issues getting this thing going that its not even funny anymore, so it figures that surging is my next issue, also it only does this at lower RPM crusing. I have been chasing this issue for quite some time spending alot of time and money to no avail, so any help and insight would be greatly appreciated. I know that one thing could be causing is the egr valve/solenoid I just have been trying to stay away from removing the plenum/runners as long as possible as I would like to do an injector swap later this summer and really dont want to do it twice, I will do though if need be. The engine is stock as far as I know, miles are unknown. I am getting good fuel pressure. No codes.

things ive replaced

Plugs
Wires
Dizzy - also had new module
ECM
Cap
Rotor
FPR
Injectors have been cleaned awhile ago
IAC

Others that i cant remember at the moment

If there is a vac leak I havent been able to find it,


is this something that a Map could cause?

how bout a coil?

 

A wandering MAP signal could cause it, as well as a wandering TPS signal, or a sluggish IAC. Depending upon the programming, you should be able to adjust the target idle deadband and minimize and hunting. What RPM ranges are involved?

 

ya know I didnt think about the IAC because its fairly new, but when you blip the throttle it sounds like it is "gulping" a fairly large amount of air. the surging occurs at roughly (under load) 1000-1400 RPM.

 

there is a coil pickup in the distributor that could be bad. also is the car an Auto or Stick

 

I hope its not the pickup coil, the Dizzy is about 2 weeks old, tranny is auto.

I adjusted min air today, car wouldnt Idle with IAC disconnected got it to idle then it started hunting with IAC unplugged, plugged IAC back in reset TPS now it runs terrible, surging is worse but I got a little better top end.

 

Are you still using the TBI fuel pump? If its converted shouldn't it be swapped as well?

 

The fuel pump is correct for TPI, I have 44 PSI @ Idle, 50 @ WOT.

 

Update,

Repalced Coil, problem persists

Fuel pressure is good, removed vac supply from FPR vac line, pressure went up.

While at Idle I unplugged O2 sensor hunting stopped. dont know why.

Surging is getting really bad now.

 

Unplugging the O² removed the feedback to the ECM. In that mode, the ECM will revert to lookup tables for fuel and spark management. Since it evidently runs better that way, something in the feedback loop is making the ECM unhappy.

When in open loop mode (O² disconnected) the ECM manages fuel based largely on TPS, MAP, coolant temperature, and RPM. To a lesser extent, it uses IAT/MAT information, and I'm not sure if the EST will be active in that mode, but the EGR and AIR should revert to default conditions.

If you disable the EGR, make sure the AIR is not porting air to the manifolds (leaking past the valve), and bypass the EST, does the engine RPM still waver with the O² connected?

 

update,

saturday i tood the IAC out and grounded the diagnostic terminals on the ALDL, the pintle on the IAC shot out of the IAC, after that happened I cleaned out the passage for it. Sunday I got to thinking, "My car at Idle was very noisy (sucking in massive amounts of air) untill it warmed up, I wonder if I had the wrong IAC". That being said I went out to my storage shed where I have a TBI manifold for an 87 Caprice. I took out the IAC cleaned it up a bit, and installed it into the camaro. Right away the car started and I heard the large amount af air being sucked in, then as quickly as it started it was gone (IAC reset).

That being said MOST of my surging is gone, it still does it whenever it feels like it but its nowhere near as bad as it was and not nearly as often. I did however get a code 43 right away, but Ill check on that later today or perhaps tomorrow, I also think that maybe this will clear up the rest of the surging.


Vader,
The car is still hunting mildly with the O2 connected, how would I go about disabling the egr?

 

Update,

I put in a new IAC and TPS, surging persists. also Ive had really bad misfiring a couple times with no warning, itll hang aroune for awhile then as quickly as it comes it goes away??? Im starting to think it may be the ecm (again)or prom.

 

Update,

I decided to take one of the AIR hoses off and the surging went away completely. Now my question is where does the AIR hose go???


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