I am new the these forums but was recomended by a friend to visit and get some help with my L05 350. I am stumped as to what the problem might be.

Problem: Car will studder and want to stall when giving it about 10 - 20 percent throttle (between 800 and 1300 RPM). Anything more or less and the car will act just fine. When cruising down the road of anything less than highway speed if I let off on the gas it will act like its going to stall for about 4 seconds and then return to normal. There seems to be a certain range where the car will want to stall.

Things it doesnt do: It has never once stalled on me. Even with the AC on. Its dropped to about 300 RPM's but then recovers. It wont do any of the above problems when the car is cold. Say below 130 - 140 degrees. Once its warmed up it then runs like crap. I dont have any starting issues, or idle issues. Even at 10 below zero this year it started just fine.

What I have done: I replaced the fuel tank(not related) but while it was out I replaced the fuel pump and screens. Replaced the fuel filter. Replace both injectors. Complete tune up and new K&N kit. I cleaned the carb out really good. I dont think its the O2 sensor as I did unplug it to test it and it ran the same.

I really dont know what the problem could be but with my performance exaust it actualy sounds embarasing when I let up on the gas and it acts like its gonna stall.

Any ideas would be wonderfull.

Thanks very much

 

I can think of several things but I'm not enough of a troubleshooting expert to tell you which is most likely.

First, if the TPS (throttle position sensor) has a dead spot, then the sensor will give the ECM a false reading.... so the wrong fuel will be delivered. The TPS has a prescribed voltage vs angle spec that might already be posted here on TGO... but it will be in the FSM (factory service manual).

Second, check the coolant temp sensor. IIRC the resistance vs temp chart has been posted on TGO before, and you can measure the elec resistance with the sensor installed by using a DVM and some tiny jumpers. IIRC when the sensor is toast the failure mode tells the ECM that the engine is very cold and it delivers fuel to suit that temperature. In your case, when the engine really is stone cold, it's ok... but once the engine warms up, you are probably running too rich. You might also check the spark plug coloration to see if they are sooty (black).

Third, check the IAC (idle air control) sensor (clean & reset per the Tech pages here on TGO). HTH and post back when you get it solved.

 

ignition control module

 

I will be going to nappa to pick up a new TPS. I think its actualy the original. The car has over 100K on it so its probably time to change it.

As far as the IAC I remember at around 75K it being changed, so hopefully that wont be the case.

Now why would the ICM go bad? and is that soemthing thats hard to change?

Thanks for your help

 

I have tested the IAC and the TPS. Both are working within their normal parameters. I dont believe there is a way to test the ICM but I could be wrong. Any other ideas out there? I heard somthing about the purge canaster might be bad. In fact On my 90 TPI iroc I had a similar hesitation at low throttle, but it never wanted to stall as bad as this TBI.

Thanks for the help