Rough starting w/loss of speedometer

This is a gradually getting worse problem. 89 Buick LeSabre, 3.8 MPFI, 90k. Car starts rough but only when the air is damp and it won't stay running (RPM 500 and rough) at those times. The speedometer stops working at the same time, the voltage will drop also. After a few miles or so, there will be a sudden jolt of power out of the engine and then all is fine (idles then at 800-1000 RPM) and the speedometer starts to work again. I have changed the VSS, the Alternator, and battery, What should I do next or throw in the towel and take it to someone so I can atleast get the codes off the computer. Needless to say I just moved to a plac where it seems to be foggy at least 3 days a week. The rainy season just started also.

Sounds like a ground problem I assume you have gone over all those especially to the engine sensors and block. Not sure this applies to this year but look under the carpet l/s of floor near the outside area of the drivers floor, possible bad ground junction there where the floor gets wet.

Believe it or not, The root of the problem is weasels:banghead: . They seem to love to chew on spack plug cables of GM and Ford products. VW and BMW are not on thier menu. I am going on my third set of cables, but before I install them I need to shield them completely.

Believe it or not, The root of the problem is weasels:banghead: . They seem to love to chew on spack plug cables of GM and Ford products. VW and BMW are not on thier menu. I am going on my third set of cables, but before I install them I need to shield them completely.

But would that explain the speedometer problem? (unless those things chewed on the VSS wiring too...)

My '91 had a rough running problem w. check engine light w. loss of speedometer, and the problem ended up being the engine computer. It started with the car wanting to speed up at 40 mph on level ground, then a month later, loss of speedo + check engine + rough running + coolant fan turning on and off...

- GB

You are correct on that that they weren't chewing the VSS wire. I had my mech look one more time at it and we replaced the idle air control and the car is running better and no looger starts rough, but I still lose the speedmeter occasionally. I just really need to take the advice first given and go through all the ground connections.

I ran across the exact same problem with a Regal, it was the computer. Rplacced it, and all is good.

Ok, replacing the ECM, anything important to know besides what the Haynes manual tells me? Should the PROM be replaced at the same time?

I've had good luck with remanufactured ECM's offa Ebay...I've also had good luck with one from a wrecked car.

ECMs in general come with a new PROM chip, but it is a good thing to ask before you buy. Otherwise, all you have to do is remove the passenger side hush panel, unclip 3 electrical connectors, one 10mm bolt, slide it out, and repeat in reverse with the new one.

I had a Park Avenue with the same problem, it turned out that the ECM was bad (much like your problem sounds to be). Another possibility is that the electrical connections are just loose and the occasional jar knocks them back in long enough for the speedo to work for a bit.

The speedo will mainly stop working a couple of blocks away from my starting point and occures usually on days when it is raining or just highly humid. If I restart the car, the speedo comes back to life. Sometimes I can drive a few miles and the car will jolt, dash indicators will flash once, and then everything will be fine. This really only happens only 2-3 times a week. I started pulling the ECM and then the wife wante to go so I put everything back in place before I had a good chance to inspect everything. I just need to save up a little cash before I purchase a rebuilt ECM, but it's next on my list.