[RESOLVED] Timing...Jumped tooth? [No, bad ISC]

[DarthBulk]

I have a question before I take off my lower timing belt cover to check my timing alignment. A short while ago, my car was running fine, and then one day I drove to lunch and when I restarted the car, it would start fine but not idle. As long as I kept the throttle open a little, it would run, but if I took my foot off the gas it would just die. When I start the car, it almost sounds like the timing is too advanced, like it will fire and then resist itself from turning over (slightly). It always DOES start, and sounds ok when I give it a little gas. It was near impossible to drive home with it dying every time I took my foot off the gas to shift or come to a stop, though. Well, I checked my timing belt and here is what I found.
With the cam gear marks aligned, my crank pulley mark is about at 10 degrees BTDC. Isn't this supposed to be closer to TDC? Is it possible that my timing belt jumped a tooth on the crank sprocket? I was going to pull my lower timing cover to check this, but I thought I would check if anyone has some input before I do that big job

I guess I put this in the wrong section...can anyone move it to the correct section please?

I investigated this problem a little bit further, and now I don't think the timing belt has jumped. I plugged a computer into my AEM EMS, and here is what I found.

I loaded up AEM PRO and connected to my EMS. On starting the car, I watched the gauges on the home screen, and I noticed that when the car was idling, the timing would be way advanced...like 35 or more. I watched as I started the car, the rpms would go to 1200 or so, and immediately start to drop. As they drop, the timing keeps advancing more and more to way above 30, then the rpms start to come up a little, and the timing backs off, then the rpms drop again, and the timing advances, and the rpms start to come up again, and this goes on and on as long as it catches the idle before it dies out. It seems like idle surge from the OEM ECU days. I know that can be caused by a bad ISC.

Can someone point me in the right direction to start troubleshooting this issue? Any hints as to what would cause the idle to go away, with no changes in my tune? My guess is that something mechanical is failing, and there is not a problem with my tune in the EMS since it was professionally done and worked fine for 3500 miles. Any help would be appreciated!

Oh, and one more thing, and I don't know if it is relevant. I got pulled over by a State trooper for having an "Amplified Exhaust" about a month before this started happening. I have a Thermal Research 3" exhaust system. They made me put a stupid restrictive 2.25" muffler on the car. So I was driving with that muffler on the car for about a month before this problem started to appear. I don't know if that would affect anything, but I thought I would throw it out there.

 

[Defiant]

Stop driving. Check the timing belts. Confirm your timing and tension. If it has jumped, it will again. Next time will bend valves for certain.

 

[DarthBulk]

Thanks, I will definitely check it. Actually, I think my harmonic damper may have slipped a little, which would explain the mark on it being closer to 10 degrees BTDC. I had drawn a line with a sharpie across the rubber portion some time ago, and now I see that line has shifted about its own width to the side. I guess I need a new one of those.

I am still running through a long list of things to check with my AEM and sensors, and I am leaning toward it being a problem with that now, instead of the timing having jumped...even though that is what it acted like, at first. I think some sensor is failing, or has shifted its zero point to where the AEM doesn't realize how to correct the idle anymore.

Ok, I figured it out. After connecting a computer to my AEM system, I found that I could not control the ISC motor (By adjusting the "Idle % vs Target" graph), so that told me that the ISC was not working. Sure enough, I pulled it off and found that there was an open circuit between pins 1 & 2. The other four coils were ok. I put on a different ISC that I had laying around, started the car, and found I could once again control my idle with the AEM software, and now the idle is fine.

The reason I thought the timing was off was because the AEM EMS would advance the ignition timing to try and catch the idle as it was dying. When I would try to restart the car, it was still way advanced, which made the car fire early and then kill itself. I know the sound of trying to start a car with the timing too advanced from working on my Fiat X1/9. It also didn't help that my harmonic dampener pulley seems to have slipped a little, making it look like the physical timing is advanced (which made me believe the timing belt may have jumped).

So, now I order a new harmonic dampener and a new ISC motor....