90 Grand Voyager intermittant problem

[Lomitus]

Greetings,
I have a 1990 Grand Voyager with a very intermittant problem. It has a 3.3L with 4 speed tranny and 200K+ miles. I've had this van for about 5 years now and I know at one point the engine was changed as all the tags say it came with a 3.0 and not a 3.3 so I don't know how many actual miles are on the engine. When the problem occurs, basically it's like the van almost doesn't know what gear it's in. It gets really jerky, stalls when I come to a stop and you have to "juice" the peddle to get it moving again. When it's in park or neutral, the engine runs fine (and starts fine as well) but as soon as you put it in gear, it tries to stall. The problem happens to varying degrees...sometimes it's not too bad, sometimes it's really bad. Once I get it up to 35 mph or more, it's not bad as long as I hold that speed, but if I slow down and the tranny starts to down shift, it gets jerky again and stalls when I stop. To give you maybe a better idea of what I'm talking about, when I come off a stop, it's almost like driving a car with a clutch and trying to start from a stand still in second gear. Slowing down is the same way...again it's like down shifting to the wrong gear with a clutch....gets all jumpy and jerky and tries to stall.

Now when I say this problem is intermittant, I mean it's REALLY intermittant! MOST of the time it runs just fine. Sometimes I can go for months without this problem occuring at all. Sometimes it will happen one or two days in a row and not do it again for a while. Sometimes it will do it every day for a couple of weeks and then it won't do it again for a couple of months. Usually it does it within 5 minutes or so after the first start of the day...but not always (it has happened after the engine is completely warmed up). Usually it only does it for about 5 minutes or so...but it has done it for as long as half an hour. Outside temperature doesn't seem to be a factor...this has been doing this for quite a while now and it doesn't seem to matter if it's spring, summer or winter.

I'm pretty sure this problem has to be something with the electronics...a gooffy sensor or something, but I'm completely baffeled as to what to look for. Since this problem is sooooo intermittant, I can't really take it into a shop for diagnosis either as by the time I get there, the van isn't doing it any more. I consider myself to be a pretty fair mechanic and I've been working on cars for over 20 years. Once I know what the problem is, I can usually fix it without too much problem, but this one really has me stumped.

Any and all suggestions would be grately appreciated!

Jim Walczak

[webbch]

Symptoms point to one of several possible locations
1) crank and/or cam position sensor acting up periodically
2) speed sensor
3) ignition coil???

I'd think it'd be rather difficult to diagnose the crank or cam position sensor, but it would be at the top of my list for suspicions. Maybe try playing with the wires while the engine is running and see if you can re-create the problem.

For the speed sensor, do you notice large fluctuations in the speedometer that couldn't possibly be occurring when the problem strikes?

[RIP]

Ditto to all three. The nice thing about the crank/cam sensors is they can be had for less than $30 a piece. I recommend OEM sensors from the dealer. Seeing any high speed issues like sluggishness or hesitation? Could be a fuel pump. Stalling at stop signs could also be an idle air control valve if equiped. Service Engine light?

[Lomitus]

.Well, there aren't any fluctuations in the speedometer. As far as high speed issues, normally I don't have any problem with that. Now when the problem is occuring, if I'm on the highway for example and I try "jumping on it" to get into passing gear, then it does get a little jerky again...the tranny shifting thing. If I'm keeping a constant speed though, it seems like it runs fine...until I start slowing down at least.

I don't think it's the ignition coil...if it were, I'd think that the problem with stalling and such would still occure even with the van in park or neutral and again, it doesn't. The speed sensor has crossed my mind though and is definately worth some consideration. I didn't know about a cam or crank position sensor though...where exactly would that be located?

Thanks,
Jim