'92 gas jetta accelerates fine, jerks at 2800-3200rpm

Hi,
I tried to find similar symptoms to mine on this site, some similar but not enough for me to go 'ah-ha!'. If this sounds familiar, and you've managed to solve it, I'd love to hear from you:


Car was running fine (this is the '92 Jetta, gasoline 1.8L engine). Just in the last couple days, when driving along it'll jerk like I took my foot off the gas (which I haven't), then not quite a second later, kick back into powering mode. It'll do this back-to-back-to-back-to... so the whole car is jerking front to back. The slowdown is just as though the car was doing engine braking (ie. foot off gas), which, if it is planned, and only happens once, doesn't disturb me in the slightest. The going back and forth though, which I have no control over, isn't nice. As soon as I take my foot off the gas and put the clutch in, the engine seems to be fine. It idles fine, the problem doesn't come up if I'm accelerating steadily (acceleration is good and powerful). It's just shown up (with the cold weather, coincidence?) so I haven't had time to fully figure out how and when it appears. So far I've figured out that if I keep it reving fairly high (4000ish) while driving, that it occurs a lot less, when I'm down around 2800-3200 rpm it's the worst. A the very start, it seems okay, but after a couple of minutes driving, re-appears. I just replaced the spark plugs (after it was doing this). The ignition cables are less than a year old (it ran fine last winter). Any ideas, suggestions? I'm well-inclined car-wise, but have replaced enough perfectly good parts (when I thought they were the source of the problem) that I'd rather get the issue on the first try (or second, or third, but with the least wasted $).
Thanks

PS. I'm in Canada, but I have no idea if our extra gas additives (for freezing) do anything about water condensation in the tank (it did run all of last winter without problems - completely stuck throttle not-withstanding)

It sounds like a shot of air might have gone through the fuel line. It could also be a cracked air intake hose that jiggled and caused a temporary loss of vacuum. I'd check your fuel pressure (I think it's supposed to be ~45psi) and I'd check the air intake and vacuum lines. If your fuel supply pump (the one inside the fuel tank accessed from inside the trunk) is going out, your fuel pump may have been starved for gas. If your fuel pressure is ok, I'd check the flow on the fuel supply pump as well.

Hi Mumble,

I have a 91 Jetta that seems to be experiencing the same thing that you were with your '92.

Were you ever able to fix the problem? Was it the Fuel line?

My 91 Jetta had the same problem last month. what i had to do to fix the problem for mine was to disconnect the full throttle switch. I don't know if this will help for every case but its something to try for a processive elimination