Very Rough, Low Idle and Missing - Help!, 73 D-Jet - SOLVED! Options

[ThinAir]

RRC is only a couple of weeks away and I'm beginning to get desperate that I'm not going to be able to drive my 914.

When I posted this, my problem was just that the idle would hunt, but otherwise it drove well. After reading the responses and reviewing Brad Anders' stuff again it made sense that my hunting problem was probably that I was just running lean. I turned the ECU 3 clicks clockwise to see if that would improve things, but it didn't seem to.

Well, things have gone from poor to bad. Right now I've got a car that barely idles at all, and when I'm accelerating or driving on the highway it often bucks/misfires. I haven't run it long enough to get it warmed up. I've tested the AAR by pulling the supply hose and it seems to be working. If I remove the AAR output hose the RPMs go up to 1000 so perhaps the AAR isn't opening fully.

I've measured the ohms on the CHT at 124 so that's within range, and I've got a brand new 270 ohm resistor inline. I have 3 MPS units that all pass on resistance and vacuum and changing them makes no difference in the behavior. I've also recently replaced the spark plug wires (not to solve this problem, but just because) and I've made sure that they are as far away as possible from the MPS unit. I've also checked every electrical connection that I can find.

Sorry that all that is so long - any clue what I should be looking at? I'm beginning to panic (IMG:style_emoticons/default/blink.gif)

[JStroud]

The bucking and misfiring at speed might be the contacts in the TPS, if they're worn might need to move them to a better path and adjust it. Helped on mine with similar problem. Good luck.

Jeff

[Michael N]

The bucking and misfiring at speed might be the contacts in the TPS, if they're worn might need to move them to a better path and adjust it. Helped on mine with similar problem. Good luck.

Jeff

I agree with checking the contacts at the TPS. I had this gremlin for a while and was checking things in the engine compartment with the engine running. I bumped the wires leading to the TPS and the idle improved. I unplugged the cable wiped the contacts and have been good for years. Good luck.

[ThinAir]

The bucking and misfiring at speed might be the contacts in the TPS, if they're worn might need to move them to a better path and adjust it. Helped on mine with similar problem. Good luck.

Jeff

I agree with checking the contacts at the TPS. I had this gremlin for a while and was checking things in the engine compartment with the engine running. I bumped the wires leading to the TPS and the idle improved. I unplugged the cable wiped the contacts and have been good for years. Good luck.

When writing that novel-length post last night, I forgot to mention that the TPS board was replaced last year with a unit from one of the board members. The connection to the TPS is one of the things I've checked, but I haven't tested with the wire pulled off. Also, I'm running the same Pertronix that I've run for ages.

This morning's behavior was somewhat surprising. Air temperature is mid-50s. When I start the car it idles at about 900 (not higher like it should since the AAR should be open) and it drives smoothly. About 10 minutes into my 20 minute commute it starts hunting when I stop for a red light and I feel a couple of slight bucks when driving, but nothing like what I had previously experienced. Even the hunting behavior seemed to go away within a couple of minutes. If it had run like this all along I probably wouldn't even have been looking for a problem.