Possible ECM issue. please help!!

[TheRutSlut]

I have a 350 TBI. At low rpm it will act like it is about to stall then suddenly it revs up on its own. I have changed injectors, MAP sensor, checked for vaccum leaks, replaced intake gaskets, etc. The only thing that makes it stop for a while, ( 5-10 intervals of running and driving) is engine at 0 rpm, key switched to acc., disconnect negative cable from battery for 30 seconds to a minute and a half to reset the ECM, reconnect negative cable, turn key to off position. After doing this it runs perfectly, not a hint of a miss or intermitent rpms. What could it be that is flipping out the computer? Or the computer itself?

 

[Keitha]

Sounds like a stuck EGR valve to me.

 

[Russell]

Agreed ^^

New doesn't mean that it is the right one or even any good if it is. Make sure you buy an AC Delco piece as the aftermarket stuff sucks.

 

[tfitch03]

EGR valve is an easy fix. Changed mine last month and it runs much smoother. I was having a similar problem as you...very high idle when the engine was cold.

 

[diesel4me]

EGR valve can cause that,but it should not be active until the engine warms up-unless its stuck open or has the vacuum hoses misrouted and its getting vacuum when it shouldn't..

Vacuum leaks can cause it to idle very low and then surge higher,when the computer compensates for the low rpm reading..idle air valve can do it too..

 

[Carcinogen]

....Vacuum leaks can cause it to idle very low and then surge higher,when the computer compensates for the low rpm reading..idle air valve can do it too..

This was my first thought also. I had a gunked up IAC on my 03 s10 and it would surge at low rpm, a quick cleaning fixed it right up.

 

[black dawg]

check fuel pressure.

 

[TheRutSlut]

I left cleaning the EGR and IAC off of my list. And if it was fuel pressure, would the computer not try to compensate for lack of fuel all the time? Even after resetting the computer? After it is reset it runs like new.

 

[ktmoutfront]

TPS. Had the same issue. My plug was broke. Ran fine otherwise. Idle sucked.

 

[dyeager535]

Computer can try to compensate for fuel pressure in a roundabout sort of way, but it doesn't "know" what the fuel pressure is, and can only compensate so much.

Disconnecting power to the ECM fixing the issue (apparently only temporarily) is a bit unusual, but there is obviously a reason. You can just pull the ECM fuse FWIW. I've never seen anything more than about 10 seconds being necessary.

Does your check engine light work properly? If so, can you narrow down under what conditions it is triggered it to start running bad again?