Rough Idle and Misfires on Warm Starts

[tragdor]

I have an idle issue that I have been battling for some time. Here's the scenario-when the car is warm, as in close to or at operating temperature, and I start the car, the car idles like shit between 300-600rpm, and then misfires if I rev it at all. This problem has progressively gotten worse. Before it would rarely happen. Now it always happens. The really odd thing about it is that after about 3-5 minutes, the problem clears up and the car idles close to normal, minus a slight idle surge. To date, I have replaced the ISC and the fuel pressure regulator. The ISC seemed to improve the condition temporarily. The new AFPR had no effect on the issue and did not improve it. My ECU has also been repaired and was tested in working condition by Steve. I wanted to get some opinions on where to go from here. What I can't get is why it is a temporary issue that clears up on it's own. I can't figure out why it clears up. Then if I turn the car off, and immediately restart it, the problem is back and follows the same timeline. The car also seems to go really rich when the problem occurs, which is why I thought the stock fpr could be bad. Can anyone offer up any suggestions? Thanks!

 

[Colt4G63 also]

Do you have a way to log? Check your LTFT! The ECU goes open loop for a little bit after startup, and it could be working off a scewered fuel trim for those moments. Maybe your LTFT is out of range. If it's adding or subtracting fuel at or near the limit, that could offer clues about what's going on. Check the actual fuel pressure with a gauge. Make sure your O2 sensor wakes up in a reasonable amount of time. Boost leak test. Do a sanity check on all the sensor readings (if the coolant temp says -50F that would be considered an insane reading).

 

[luv2rallye]

Sounds like the classic hot start/vapor lock problem: http://www.dsmtuners.com/forums/newbie-forum/217349-vapor-lock-hot-start.html

 

[Colt4G63 also]

I don't think it's vapor lock because he said it happens just as badly even when he turns it off and back on instantly. Wouldn't vapor lock take a few minutes to set in?

 

[tragdor]

The sensors look good and read normally. That's why I hadn't replaced the coolant sensor yet-I thought it was still good. I have Jackal installed right now and am able to log. The problem was present before making the switch so it is definitely not SD related. I installed a AFPR last night and it made no difference on the problem. I will check the gauge and report what I find. I believe when I was looking at it last night, the pressure was rising and falling within a few PSI during the problem, but I am thinking it may be related to the low voltage being generated due to the idle being between 300 and 500rpm.

 

[stonetalontsi]

sounds like it could be an egr valve. if you still have one.

 

[tragdor]

sounds like it could be an egr valve. if you still have one.

I blocked it off about a month ago. The problem was present before that and the blockoff did not seem to make a difference. Thanks for the suggestion though.

 

[tragdor]

I pulled multiple logs. The first log was of the car just warming up. The car is really trying to find a steady idle. This has gotten worse. The second log was after I started the car and the car started idling rough. I let it run until the idle cleared up. The third log was the car completely off, then started and immediately idled rough. I let it run and got out of the car. I tried pulling the vacuum reference line off of the AFPR and left the vacuum line and the AFPR vacuum port open-it made no difference. I then capped the port with my finger and left the vacuum line open. It didn't make a difference. I then unplugged my ISC and it made no difference. What do you guys think? I'm wondering about the accuracy of my coolant temperature sensor and now wondering about my rebuilt ISC.