First... about a week ago on a cold morning, I went out and started my car ('90 RS 305 tbi A4) only to have it misfire violently. There's popping coming out from the pipes, and it shakes the car quite a bit. Giving it gas makes the popping worse, but makes it all go by quicker. It'll only do it for a few minutes, then the car will level out and run fine. This only happens on a really cold 40 degree or less morning, then it won't do it again until the following day... everyday.

Second... I was going down the road Saturday and it started misfiring on and off while driving. First real "soft" jerks... then progressively harder jerking while trying to accelerate, and it gets worse the more gas I give it and the longer I drive. Worse yet, when I try to accelerate hard, there's a hard bumping seemingly coming from under the hood. I'm not positive though. I pulled over and came to a stop. In Park, it just misses every now and then at idle, but give it gas and it gets worse. No power whatsoever. The bumping only happens in gear under hard load... it doesn't do it in Park. I limped it home, and called my Dad to come over and take a look. Damnedest thing, when my Dad got there I fired it up and it ran perfectly fine. I drove it all over the neighborhood testing it out... ran fine. My Dad thinks I imagined the whole thing. We scanned it for codes to be sure... nothing. I looked at the easy things like loose wires and hoses... nothing. I didn't have a single problem with it Sunday, but it did it again Monday... and once more on my way home earlier.


I would assume that these two problems are related, but I can't be sure. The question is... where do I start? Fuel system? Ignition? Whatever the problems are... they seem to pop in and out without a trace.


I would like for this to be fixed soon... as my other car is in storage for the winter. Also, getting a ride to work at my age is a bit humiliating. Any help is greatly appreciated.

 

Have you checked to see if all of your sparkplugg wires are attached to a correct sparkplugg???
Check your timing too, although it doesn't sound like it.
Than check your igniton components. If everything is well time to check fuel preassure and if not that, open up the valve covers and see whats going on.

I've had quite a few problems with my TBI, and I replaced almost everything, and tested even more. Its kinda hard to test some things but you should at least try and test them.
Really sounds like the wires might be in the wrong place. I had backfiring like that only to figureout that my firing order was, well... not in order .
So check that out and let me know what happens.
Also, before I go, check your sparkpluggs too!

 

I'm pretty sure that my firing order is correct, because the wires haven't been off since my last tune-up months ago. The problem just started a week ago. I'm going to give the plugs and wires a good look when I get the chance.

Timing is something I've never messed with. I'd barely know where to begin. My Chiltons can probably help me out there.

About the fuel pressure... I have a tester, but I've never used it on this car. Does TBI have the pressure valve, or do I have to go into the line? Where is the vacuum line I'm supposed to plug?

Thanks again.