Shes got the 5.7L and auto trans. She runs fine but after about 15 min of driving at full temp she starts acting up real bad. Kinda sounds like she has a mild cam ....just not in the good way...especially since shes stock. I was thinking it might be related to the auto timing advance or the egr valve. Since I dont know anything about the auto advance I started looking into the egr. I plugged the vacuum line with a BB and hooked it back up. She is running ALOT better now but still not right. Any suggestions?

 

My first thought would be the O2 sensor. When the car is cold the computer is running in open loop and the O2 sensor has no effect on the fuel mixture but once the car is at operating temperature the computer is in closed loop operation and the O2 sensor controls the fuel mixture. This is the only thing that I can think of that is temp dependent with the TBI.

 

Thanks for the help...After putting in my spare map sensor and blocking the egr...the O2 was my next thought. I will be checking it out in the morning...hopefully all goes well.

 

check my post as I had the same happen https://blazerforum.com/forum/full-size-k5-1969-1991-gmt415-1992-1994-tech-42/89-k5-gas-flooded-motor-44365/. you should have a check engine light and the first thing I would check would be the coolant temperature sensor that could be had for around $15 at autozone.

 

After thinking about it I agree I would try the Temp sensor first. The sensor may be inaccurate giving the computer bad information for fuel mixture control.

 

Worked on her yesterday. The o2 sensor was fine as was the knock sensor. Pulled apart the throttle body and was supprised that it even ran with the amount of buildup and clogged ports. I completely rebuilt the TB and replace the fuel filter ( the guy before me used brake line as fuel hose!!!) Also reset the timing as it made its way to about 5* after TDC. The EGR is in perfect working order as is the fuel regulator(after rebuild). I am completely out of ideas at the moment but will be checking the temp sensor(not sure which one you are referring to but will check all of them.)

Forgot to mention that after all this work done it no longer acts up after its hot. It acts up maybe 30 sec after I start it. She doesnt miss anymore but still chugs really bad.

 

The temp sensor for the computer should be the one by the water inlet. The temp sensor for the gage/light is on the side of the engine block.

 

does the engine check light come on?

 

I would assume so but I'm not sure because the bulb is burnt or missing. I tried jumping pins A and B on the ALDL to see what codes I have but it doesnt light up at all. I am hopefully getting a new bulb for it today so I can see what codes I have.

 

I checked the IAC for a second time and while testing it the center part shot out. I replaced the IAC and the problem is gone. Thanks for the help everyone.