Courtshark

My '88 S4 auto has sat for a while since I've been enjoying my new-to-me 5 speed. I think I last drove it in September when I posted a similar thread; it cured itself back then and unfortunately I let it sit ever since. I cleaned out the filter box and found a decent amount of debris. Thought that might have been the cause. Nope! The car was last filled with gas on June 30, 2011 (meticulous with my records) and I've driven the car 30 miles since then.

Today, the battery of course was dead, so after remedying that, I tried to take it out to warm up the oil so I could change it (I eventually got it warm enough to do so). This car normally runs like a top; used to anyway. Upon starting, if it would stay running, pushing the gas pedal would sometimes have no effect; even flooring it. The car would either stall or eventually respond to the gas input.

It idles fine, and runs/sounds fine up to 2100 RPM. Yes, precisely 2100 RPM! Not 2050, but 2100 on the nose. After that, the engine has a repeating stumble/hesitation/miss that is present at any RPM level beyond 2100. If I let off the gas, it will drop down to idle like nothing happened (9 out of 10 times; once in a while it will stall). If I try to get back on the gas while its decelerating, it will respond only about half the time. Other times I can floor it and it's as if my foot is not on the pedal at all. When running, there's a valve tapping noise from the right cylinder bank that changes corresponding to RPM changes.

During all of this, the car is not blowing out large amounts of smoke; once in a while the occassional puff, but nothing to indicate a rich condition.

I pulled the easiest-to-access spark plugs (front left), and both looked to have a decent amount of carbon build up, and were a little wet. Couldn't tell if it was oil or fuel, but I'm guessing fuel. Could it just be flooded? I've given up for the day and will try starting it in the morning. Or should I wait longer?

If it's not just that it's flooded, I'm thinking it could be: distributor caps & rotors, spark plug wires, spark plugs, clogged injector(s), failing fuel pump, jacked LH computer (current has an ECU with Autothority chips in it; could try swapping over the one from my 5 speed), bad MAF (I believe the one on the car has been rebuilt; can't recall at the moment), or a clogged fuel filter. Before I engage in this witch hunt, where should I start?

m750rider

I agree with circlex, a bad coil wire will act just like this, and if it is finding it will be easy in the dark. Check it first.

Stromius

Could also be corrosion at the coil connection. I found a bunch o green fuzz on the passenger one which resolved my 88's stumble. Since there is no limp mode on <89, unburned fuel gets to the cats so best resolve asap.

Courtshark

Thanks for the responses guys! Looks like I'll be starting with the coil wires. Will report back. Unfortunately I've picked up a stomach bug or something, so I won't be wrenching today. Ugh. Car has a bug, I have a bug... not cool.

Courtshark

Didn't see any fireflies. Wires look fine, actually. What is the expected lifespan of the coils? Not sure if mine are original but I think they are. And wise to do both at the same time? I assume so, especially because I can't see anything outwardly wrong with either one.

An additional observation: runs much better in 2 than 3 or D. I can run it out to 4k Rpms or more without the stumble or hesitation, but if I let off the gas, I cannot get back on it right away, if at all before it stalls. In 3 or D, I can't really get the Rpms above 1500.

Courtshark

Getting pretty frustrated at this point... after cracking one of the spark plug boots and getting that replaced, I changed out all the plugs; no difference. Cleaned all of the distributor contacts, no difference. Coil wires look fine (but maybe they are bad internally?). No obvious corrosion on any of the wires. Added a bottle of Techron; no difference. Topped up the tank today with fresh gas (it took about 8 gallons), no difference. I just read through DocMirror's similar thread, and in the end for him it was apparently very bad gas. I guess I need to run through this tank of gas? Brother thinks it might be a bad fuel pressure regulator or dampener. He had a similar experience with his '83 944 and that's what fixed it (can't remember which of the two).

At this point, I'm ready to give up and sell it as is. Seriously; someone make me an offer. I am tired (ok, exhausted) of messing with this and I really don't have time for both projects.

Courtshark

Added some Seafoam gas treatment, didn't seem to make a difference. http://www.seafoamsales.com/tech-info-gas-engines/ The fuel pump, however, seems to be whinning a little louder than normal. At this point, I think it's the fuel pump, one of the fuel pressure dampeners, or one of the fuel pressure regulators. Or it's a perma-Gremlin I will never find.

Ian Firth

try unplugging and replugging the MAF sensor connector.

My 89 GT would run fine, and then suddenly go all fluttery. I could get it up to 2000rpm by gentle revving but then it would die unless I was really quick getting off the throttle, in which case it would idle. I tried plugs, and a bunch of other stuff, but finally decided to try to see if the MAF sensor was misbehaving. So I unplugged the sensor, started it and ran it, which made things marginally worse, with a terrible misfire at 2000 rpm. But I could slowly get it through the misfire and then it would rev out, not cleanly but not bad. I replugged the MAF sensor and it has been running ever since. I looked at the connector and it was as clean as the day it was built. No guarantees for your situation, but worth the 2 hours for me.

Cheers, Ian

SeanR

Can you swap in some new or known good ignition amps? Those are the things being the bumper, drivers side, under the black cover.

Stromius

Courtshark - How's the MAF plug? Boot soft or old/hard/cracked?

Mine:

Courtshark

Wow, let this go for 3 months... been working on the Kraken.

Anyway, after bleeding the clutch... no, wait, it's an automatic...

it turns out the MAF was indeed bad. Not the connector; the MAF itself. This unit was a JDS/928sRUS replacement from '08; swapped in a different one and boom, runs like a champ. Time to put 'er up for sale!

TheVeryOldMan

My 90 GT stumbles even on constant throttle, flat road but not always. Perhaps 1 trip out of 20 exhibits this problem but the rest of the time it runs perfectly. I'm going to check the MAF as well as watch it run in the dark. It's maddening because I sometimes feel that it is going to quit and going up a mountain hwy is not when you want your engine to stop.