I just recently acquired a 1990 Lesabre with 150,000 miles.

It drives great until it warms up good (about 10 miles or so of driving) and then it starts the hurky jerky thing. Lights come on the instrument cluster, the speedometer goes to zero and it is missing and coughing for several seconds.
Sometimes the speedo will read 0 when the car continues to run and miss, sometimes it hops between the speed it is going and 0.
It sometime clears itself and drives fine for a while before doing it again. Most of the time, if you take your foot off the gas during one of these episodes it will die and need to be restarted (this includes driving down the highway at 65 mph. One time it did the hurky jerky thing with my foot on the gas pedal until it died while driving at 65 mph, but usually it will keep going if your foot remains on the gas pedal.
If I'm going slow and it dies, it will,fire up and run again. If you simply put it in neutral and start it, unless my foot is on the gas, it will die immediately again. If you stop turn the key completely off and then back on, it will idle and run OK but it seems to be missing.
If you turn it off and leave it for a while, it will start and run great until it warms up good again.

I thought that it was fuel filter so I changed it. No change in the behavior of the car.

Any opinions on what the issue(s) are? No check engine light and no trouble codes. I'm thinking ECM..........anyone agree or have any idea's?

Thank you for your help in advance, I appreciate whatever info you can offer.

 

Do you have access to a fuel pressure test gauge? You can test the fuel pressure when its cold at key on, engine off, then key on, engine running, and do the same after it warms up and you have the issue.

You can also check the fuel pressure regulator by pulling the vacuum hose off the top, and look for anything leaking around it, and for the smell of gas.

 

I was driving it again this morning. Same kind of stuff but the check engine light kept going on and off along with the alternator light, and some of the other lights on the console. It would run, die, run die, for about 30 seconds or so. The speedometer stayed at 0 the whole time.
I pulled to the side of the road, turned the key off and back on and it started and run fine for about a half mile, then died. I fired it back up and it ran fine until I got to work.

I appreciate the response. I'll get a fuel pressure gauge and see what I find out.
It's kinda weird though with the instramentation board going haywire, I was wondering if its electrical.....but when its running and dying and running poorly, I can see why it would behave this way.

 

Do you know where the crank sensor is located?
At the passenger side of the engine just behind the crank pulley.
If you can get the car to act up while it is parked with the hood open,just pour some cold water on the crank sensor . if the problem stops right away , change the sensor.
You will need to remove the crank pulley to do this , but its not a difficult job to do.
There is a plastic grille you can remove from the inner passenger fender well to get good access to the pulley bolt. Also it helps if you remove the RF wheel.

 

For your instrument panel issue, check the battery cables for corrosion/loose connections. Peel back the plastic/rubber boot over the ends to check for corrosion there too.

 

If it's acting up, it wont idle. I'd have to have two people to be able to pour water. I've also heard from a friend that this may be my issue as well, but he' said the repair is quite involved. I'm a backyard mechanic at best, but perform whatever repairs I can myself.


As far as my instrument panel goes, its really weird. The only time that it malfunctions is when the car is coughing, missing and dying. The car will actually kinda be running (sputtering and coughing) and the speedo says 0 going 65. Sometimes it will jump up to the correct speed, sometimes not.

Turn the key completely off and then back on,......whoola, it will run decent again......for a short time and the fun begins again.

 

Check out that ign switch under the dash attached to the steering column.

 

I've been looking into the easy stuff trying to troubleshoot before I started turning bolts.
One of the many things I tried was that I unplugged the pigtail on the EGR valve and drove the heck out of it. No problems and it quit the hurky jerky thing when I drove it for about 60 miles (usually is starts acting up within 10 or so miles). I tried to start it without it plugged in this morning and it wouldn't run so I plugged it back in and drove it for quite a while without any further problems.

I'm now about 98% sure that my problem is a malfunctioning EGR valve.

 

If it is only the EGR valve, you are getting away cheap. Let's hope your diagnosis is correct.

 

Diagnosis was terribly incorrect.

I haven't drove it for quite a while.
I jumped in and was driving it around and got it out on the interstate going 75 plus mph. It started into the episode and continued for quite a while.
Some different but same issues. Check engine light flickers and the temp light came on. The speedo went to "0" and stayed there for the most part even when it wasn't missing and coughing this time. It stayed running for quite a while this time with lights flickering on and off (check engine and temp). I pulled off the interstate and it died. I put the tranny in park turned the key completely off and started it up and it ran great. The speedo worked fine. I drove it another 5 or 6 miles home without another issue and it's been parked since.

With everything going haywire like that, could it be the ECM? Or, should I plan to replace the crank shaft position sensor?