89 Tempest 2.0L --> Rough Idle :/

[MichaelS]

Hey all,

I can't seem to figure out why my 2.0L is idling so rough. I had my ignition module, ECM (except for the PROM), 2 coil packs, ignition wires all replaced, and yet it continues to rattle on idle. Acceleration seems perfect, one of the engine mounts was replaced earlier this year, but my mechanic says that the mounts are ok. Plugs are less then a year old, but they have somehow managed to rust out a little. I have tried over gapping the spark plugs, which helped a bit.

Idle relearn seems to be impossible since the fan doesn't kick in after idling for 15 minutes (admittably in the cold). I know the fan works though, because field test-mode kicks it on, and if you unplug the temp. sensor, it will increase the RPM and kick on the fan...

I'm puzzled on what this could be ?!?

Regards,

Michael

P.S. I had the priviledge of using my mechanics scan tool (OBD 1) and looking around at the data that the ECM is seeing. From the top of my head, all I can remember is the car is idling between 800-1200 (NOT in a erratic loop), something about another idle that was set for 075, the coolant temp was in the high 90s (celsius), the IAC count was in the mid 20s, MAP was about 35kpa... vacuum lines look ok, there was a leak, but that's fixed now.

[Jim_I]

Okay, you know the ignition system is good. We're assuming all wiring and all sensors are good. If that leads to nothing is it a surge? Or a miss? If it's a miss, Pull the spark plugs, and check for colour, the electrodes should all be a chocolate brown color, while you have them out do a compression test, cylinder compression should be all be within 10-20% of each other. Try this and see what you can find. Is it an overhead cam or a pushrod 2.0L. If it is a overhead cam and your compression is good but 1 or 2 plugs are off in colour (black or white) it might be an injector problem. Your widening of the spark plug gap makes me think it's a compression problem. On early to mid 90's GM vehicles a diagnostic scanner will tend to raise the idle, we don't know why but it just does.

Jim

[MichaelS]

Originally Posted by Jim_I

Okay, you know the ignition system is good. We're assuming all wiring and all sensors are good. If that leads to nothing is it a surge? Or a miss? If it's a miss, Pull the spark plugs, and check for colour, the electrodes should all be a chocolate brown color, while you have them out do a compression test, cylinder compression should be all be within 10-20% of each other. Try this and see what you can find. Is it an overhead cam or a pushrod 2.0L. If it is a overhead cam and your compression is good but 1 or 2 plugs are off in colour (black or white) it might be an injector problem. Your widening of the spark plug gap makes me think it's a compression problem. On early to mid 90's GM vehicles a diagnostic scanner will tend to raise the idle, we don't know why but it just does.

Jim

I'm terribly sorry for not replying in a timely fashion -- i've been trying to cluster 3 computers, and things didn't go as planned (gotta love Linux )

This week I noticed that a vacuum line was cracked, upon trying to fix it, it cracked on me a few times. Temporarily, I taped up the vacuum line that goes into the splitter (under the firewall). This lowered the idle and smoothed it out for about a day. The car now idles at (what sounds like) 1300 RPM... This morning I connected the vacuum line back and its still idling high. Last night I did get a code 24 (which points to the VSS or circuit), but that went away after re-starting the car.


To answer your questions, I haven't done a compression test (at the moment i'm a little strapped for cash (gotta love hiked tuition), so I can't afford to get the compression test tool). The missing (before the idle went high) used to be on idle. It looked like it was coming from cylinder 2 or 3 juding by a spark tester. This 2.0 has a push rod.


A friend went out and got me some vacuum lines, so we're going to install them this weekend. Hopefully that'll fix the problem.


Thanks!

Michael

P.S. This car uses a TBI (throttle body injected) and only has 1 injector mounted at the top of the throttle body.