Uneven idle. No power.

[rydeon]

Long story short. 1990 c1500 rwd 5.7. Recently my truck died on road while driving. Always ran rich before and sucked lots of gas but still got me there. Rebuilt TBI with Diaphragm for regulator etc. Replaced temp sensor in manifold, also new O2. After this the idle surges up and down and almost dies. If i rev the throttle it runs fine. Timing is good. Possible MAP sensor? or IAC? Just also had new stock exhaust system put on. But it ran awhile before this problem. Ok so not so short. This is a 5 speed manual tranny truck totally stock. Any suggestions or laughter would be appreciated!!

 

[kennythewelder]

Sounds like TPS. You need to read your ECM codes.

 

[rydeon]

Thanks. but the check engine light was on all the time before this and now its off. I do know how to check the TPS with a volt meter so i will try that first. thank you.

 

[rydeon]

Ok its been awhile and still messing with this truck. I recently replaced the MAP sensor and IAC control on the TBI. Tested the TPS per kennthewelders advice and it checks good. New O2 sensor. Check engine light not on at idle but does come on when i get on it. Code is 43. Which if i am reading it correctly is the knock sensor. But i think i might be dancing around a weak fuel pump as it does ping when i get on it and it has low power. Fuel filter is newer and base timing is spot on at 0 with brown and black wire unplugged. Possible lean condition?? Any thoughts are greatly appreciated. Thank you.

 

[ram1220]

Check the EGR valve. My 90 Sierra 5.7l only set the check engine light on the highway after about 5 mins of driving. She ran good but at idle the rpm's would constantly go up/down. I changed the O2 sensor and the EGR valve and it solved the CEL as well as the idle issue. Since you already changed the O2 sensor you might check the EGR valve.