1992 Trooper - Speedometer problems and check engine light

Hi folks,
I have a 92 Trooper LS with the 3.2 DOHC engine. It has been a wonderfully reliable and comfortable vehicle for me these past 160k miles.
About 2 months ago, the check engine light started coming on sporadically, mainly while driving at highway speed in cold weather. It would usually go off once the vehicle slowed down to about 30 mph from 50 mph. This has continued and seems to be even more random these days - i.e. it will come on for about 2 minutes while driving 30 mph and then go off. I've had it in the shop 2x and the computer cannot find any codes to accompany this. Mechanic tells me that I need to bring it in while the light is still on, otherwise they cannot trace it. But the light does not stay on for me.
Simultaneously, the speedometer has been acting really wacky. I'll be driving 70 mph and suddenly I'll look down and it is sitting at zero. Then it will jump up and dip up and down crazily before finally settling back to normal. This sometimes happens in unison with the check engine light, but I also see the speedometer glitches more often than the check engine light.
I'm not noticing any other problems, so I've been just living with it. Has anyone seen these symptoms and know what the problem is? Do I need to get it fixed or is it ok to just let it be, considering the age and high mileage of the Trooper?
Thanks, Eric
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Thanks for the feebback on the vacuum line. Had us a little worried - and we can't find a Chilton's or Hayne's for that year.
My 92 Trooper has 177K on it. I'm not experiencing your check engine light "problem" but my speedometer acts crazy as well. Most of the time, it registers a little under 50 MPH but I have seen it do the jerky stuff going way up and then down to 0 before finally settling back to just under 50.
Thank goodness for the tach or I'd be getting pulled over all the time :)
Charlie
Eric wrote:

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I've been having exactly the same problem with my '92 Trooper for about the last year...coupled with a phantom tail light and dome light problem. Sometimes they work and sometimes they don't. Have not been able to track down a cause but somehow I feel they're related...maybe a bad ground somewhere. If anyone can point us in the right direction as far as a remedy it sure would be great.
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Its incredible, but Im experiencing exactly the same problem with the check engine light and the speedometer.
I do no know how to solve it!
Any help would be great!
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Here's an update, as I started this topic back in February. My 92 Trooper has been to the shop about 3-4 times for the check engine and speedometer problems. They kept telling me that they could not detect any problems, but I just got it out of the shop today after one more try. The check engine light had really been coming on a lot and the speedometer getting very eccentric.
Today, they picked up an EGR code from the check engine light, though they advised that the EGR was ok - so it was diagnosed that something in there needed to be cleaned. They also said my speedo gauge is shot and should be replaced, but at $350 estimated, I declined this repair. I ok'd the EGR valve clean and seems to have fixed the problems with the check engine light. The tech told me that the speedo is not something to cause a malfunction in performance - it is just a hassle and I might get a speeding ticket.
Since it is 12 yrs old with 162k miles, I'm just going to deal with it!
Regards, Eric
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