Engine won't idle?

[vonrottes]

Been having an issue the last week or two that is not consistent in when it happens..

 

Sometimes the engine in my truck won't idle cold, only happens at start up, runs fine with just enough throttle to maintain an idle speed, even at 500rpm.

but if I let off the throttle it will idle down and just stall, but start right back up.

runs perfectly fine once the ECT hits about 190-200F.

 

at first I thought it was the IAC going out, but I hooked it up to HPT and commanded 128 on the IAC steps and got it to idle around 700rpm

commanding a higher idle speed did nothing.

 

When it's doing this the fuel trims are going around -2 or -3 at start up but holding the throttle they stay around 0 to +3

 

This is something that just started, though it did happen ONCE when I tried to flash a RTT mod, but went away when I went back to a stock OS.

I've been running the same tune for a few months, only big change I've made is 14* timing at idle but that was a good 3 months ago, and a returnless fuel rail and "628" injectors back in february

 

I'm really at a loss, not seeing ANYTHING weird pop up in the scanner.

HPT and Torque pro. No DTC or pending.

[STEVE-O]

Have you checked the tps?

[vonrottes]

Have you checked the tps?

I have not, I'm not ruling anything out.

But I just replaced it fall 2014.

I will look into it though

[Cordell]

Have you logged the airflow trims? I might try adding some desired airflow or checking into your injector offset if you can't find anything "physically" wrong.

[aussiek2000]

Still running a MAF? Airflow table needed some tweaking on my car after the cam/heads. Would surge at idle on a cold start.

[vonrottes]

Have you logged the airflow trims? I might try adding some desired airflow or checking into your injector offset if you can't find anything "physically" wrong.

 

Still running a MAF? Airflow table needed some tweaking on my car after the cam/heads. Would surge at idle on a cold start.

 

 

It's running stock injector timing(from a 2004 Silverado) and stock MAF tables on a stock engine save for headers.

Like I said this is just something that happened over the last week or so.

It has apparently started doing it while hot now as well, died three times in Etna earlier.

 

I wish it would at least surge when it does it, like if the maf was unplugged or something, but it just idles down and dies, doesn't even try to bring up the idle...

 

 

I have not had time to really tear anything apart and look into the issue further, hopefully I have time tomorrow.

[cdk 4219]

Look into the fuel pressure and verify that it is being consistent when the problem arises.

[aussiek2000]

do you have HP tuners that you can get a log and post up?

[vonrottes]

Look into the fuel pressure and verify that it is being consistent when the problem arises.

if it was fuel related wouldn't the STFT go way up and injector pulse width increase trying to compensate for a lack of pressure?

Again thoug, not ruling that out so I will look into it as well.

 

do you have HP tuners that you can get a log and post up?

I do, but I forgot to save the log from yesterday morning when it wouldn't run.

if it does it again I will be sure to log it and actually save it.

[cdk 4219]

Not necessarily, I had issues with low pressure, and the engine wouldn't idle. There is not really any strategy for the ecu to look at low pressure, and if is occurs, the ecu doesn't know what it is. It's definately a place to start.

[vonrottes]

Just figured I'd let post saying I got it fixed.

Took the throttle body off, checked the TPS, cleaned the whole throttle body and IAC (which had a lot of soot in it)

also found my battery cables had gotten really loose...

 

But it's idling fine now and has not had any problems all week