groppo

Fixed one thing, and as as the law goes, now have another to do. This ones annoying. When on the road the engine seems to miss a bit. It’s not a bad miss, like I’ve had in other cars. A passenger I reckon wouldn’t even notice it. When cruising the car seems to stall a fraction, then pick up again a split second later. This happens repeatedly over a few seconds, then stops, and then restarts. If accelerator is kept still the car will lose speed. I can’t tell if it happens under load. A full tank makes no difference, nor does filling up at different gas stations or if car is cold or at operating temperature. The only work done recently is transmission work. Doesn’t sound like a clogged fuel filter. It’s getting gradually worse. It did it a day, then nothing, then a day or 2 later again. Now it happens a lot. The fuel pumps were replaced 2 years ago. So, before I tackle a number of possible causes, maybe someone can pinpoint the problem.

Also, just went to replace blower motor, but cleaned out old one first and had a win, it worked fine.

P/S. Couldn’t find any thread on this.

groppo

WICruiser

Given the quick off / on nature in your description it sounds like one of the critical relays is dropping out breifly. When you were cleaning out the blower motor did you disturbe the ground connections in the fuse/relay board area? I would start by checking ground connections and consider replacing the three critical relays as a starting point.

Mike Frye

You might also want to give more info about your car so the brains on here (of which I am not one) can help more.

There have been cases where the fuse/ce panel has gotten wet. While you were in there did you see any water damage or open anything up that could let the water in? I think there's a seal around the bottom of the fan that could be disturbed and cause moisture to damage/short some relays as WICruiser says.

EDIT: Maybe a loose wire. Check all plug wires at both ends and both ends of the coil wires. For the miss, can you isolate it while it's idling by CAREFULLY pulling one plug wire at a time to figure out which one it is?

Lizard928

I would be leaning towards too lean of a cruise AFR,

how old is the MAF (if applicable) and FPR?

SteveG

Second this. Check your coil wires, both ends. Something similar happened to me. I found corrosion on passenger coil wire. Replaced it and it cleared. HTH.

groppo

The cars a 1990 S4 so it has a catalytic converter. I’ve already had a new torque tube installed. I don’t want this one to go so, Dave, send me the service bulletin thanks.

The stalling started before I worked on the blower motor but I’ll check the relays to rule them out, isolate plug wires and check coil wires too. And there was leak from the blower fan well onto the cabin floor. I cleaned the drain out. This happened about a year ago. The stalling started a month ago. The MAF and FPR as far as I know haven’t been replaced since I’ve had the car – 7 years.

Could the problem be the high tension lead, when current jumps to bonnet? I replaced these 4 years ago including the compressors?

Getting there……..


groppo

TroppoShark

I had nonsense like this happening for a while, and I came to realise that it was when I hit potholes or small bumps. I'd had an immobiliser fitted, and the electrician disturbed the relay closest to the trans tunnel,; can't remember what it's called offhand... (I've threaded this result before if you want to search).
The relay was only leaning out about ten degrees, but it was enough to interfere every time small bumps were hit. Once I pushed it in properly, there was no more problem. I could have spent lots of dollars trying to track the problem down, instead of a couple of hours that it took me to find.
Good luck.
Phill.

fraggle

Check the wiring harness to the crank position sensor. You'll have to pull the airbox and the MAF to get to it. I'll bet it is worn through and occasionally shorting to the block.

Alternatively, if you have access to an o-scope, you can take a reading from the central electric, but I can't remember which pins at the moment. Since it is intermittant, that probably won't help you, though.

groppo

.......interesting, this morning driving on the freeway going over the slightly raised road joiners (the one's between the ashpalt and bridge ends) the problem happened. The car does have an aftermarket engine immobilser so I'll check the relay. If not that, I'll work through the list this weekend.

groppo