I have a 91 jetta, manual, same engine (RV), same problem. I also suspect my motor has been replaced, because the title says its a rebuild and that it's exempt from odometer readings. (although I dont see any clipped wires around the engine)
I have tried the basics, just like Dubljay. when I got this car it ran fine. there were a few rare times where it would stall out and wouldnt start, but then this problem developed over last winter. now, it starts right up, and runs forever at idle (until i stall it), but there is significant loss of power, it acts like there is a clogged fuel filter on acceleration, (during which sometimes initially it floods and dies immediately at a slight touch of the gas),. it will accelerate fine for a few seconds,, but then power will fade almost completely, and then usually the car will start bucking, or power comes back in the higher RPM range, or the car stalls, and wont start. one characteristic of this problem is the surging of the throttle. I know the car is going to lose its power when when I take it out of gear to shift and the engine maintains a high RPM, or the throttle surges at idle sometimes maintaining an idle of 1800 rpm's or so, or just surging from 900-1400 rpm's up and down, then dipping down to 400-800 either stalling, or almost stalling.
The car has always seemed to run too rich. when I first got the car, I failed emissions tests so I replaced the Oxygen sensor about 2 years ago which helped thin the fuel mixture, and it passed ( I didnt drive it much even when it ran)
When this problem started:
First I replaced the fuel filter (lifetime my ass) I have a fairly new air filter too I replaced a while back (K & N), and i replaced the checker auto spark plug wires with Bosch wires. that didnt help so I took this into VW mechanics shop where they tested the fuel pump, put on new spark plugs, checked a valve and some sensors, but they couldn't figure out what was wrong, so after around $200 of labor, so I had them stop. at this point the car would only do a dead stall, it didnt do any bucking or jerking, it would just unpredictabley lose power slowly and stall, So I could still drive it around I would wait until it was cooled off then it would *usually* start again. then my radiator fan switch went out, and I thought it would be a good idea to change the cap and rotor when I changed out that heat sensing switch on the radiator. The old cap was not bosch, and and it was worn, so i put on a genuine bosch cap and rotor. If you can believe it, this is when the bucking and surging started ! I expected the new cap to help get back some power, and maybe help with the stalling, but instead it made things worse, now I had even more power loss, except when it hit the high rpm's it would give me back the power I once had, (still not to the engine's potential, I never had that), then I would need to shift, and it would repeat all over again. this effect of power kicking in at high rpm's slowly wore off, and all the while the car would sometimes crap out and not start. So during that time I had a friend do a timing check at his acura shop, he said the timing was fine, and gave me two suggestions: Air flow sensor, or a clogged cat. so I went to the foreign wrecking yard and the owner helped me try several parts, my airflow sensor tested ok to me, but thats what we tried first ( got one off a 91 fox). same resistance readings, and no change in the condition. Next we tried the Ignition control module on top of the ECU housing, no change. then we tried the selenoid by the intake manifold, which i think is the EGR valve, because one hose went into the intake manifold, I cant remember where the other hose connected to (crankcase?), Still no change, so we put in a brand new in-tank fuel pump, I had a little better throttle response after, but the same sputtering occurred. then the junk yard owner suggested I try taking off the gas cap and running it, well I did have the wrong cap on, one that didnt allow air to get in, (my sister had driven the car, and she had changed the old cap for some reason) now with the gas cap off, the car didnt sputter or stall, (it sometimes has to run for a while before it begins sputtering, but I drove for a few miles, and everything was good) much to my disbelief, and I drove home from the junkyard thinking the guy was pure genius. I found my old gas cap, that seems to be a breather cap, and put it back on, (though not tightly). most days the car still didnt have the power it originally did, but somedays it would get back to its old peppy self. that great solution lasted for less than 2 weeks, and now it is as bad as ever
I am so grateful for your site where I found the same problem on the same engine.
I do take off the gas cap when it starts sputtering but that doesnt help now. So after reading your suggestions yesterday, at a muffler shop I had my tailpipe cut off at the catalytic converter to test for clogs, they couldnt find anything wrong with air flow there, and they tried to diagnose the problem but couldnt find anything. I dont have a bentley manual, just a cheap one. I would appreciate any suggested solutions to this problem, I dont think it is timing or engine related, I was looking to replace the distributor next, until I read here that that hadn't helped dubljay. I am guessing that it is some other electrical problem, or and issue with the fuel lines and/or the accumulator/regulator for those fuel lines. but right now I dont have the money to get a manual on top of the part(s) I need.
Thank you for your time and ideas,
Steve.
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