Erratic RPM Indications

[ESGrauer]

Hope yall can help out -

A couple of months ago, the RPM gauge on my 95 SL1 would suddenly die, then start varying erraticly between zero and 3000rpms. Actual engine operation was normal in all gears and idle. The service engine soon light would come on at this time. After shutting down the car and restarting, the problem and light would dissapear, only to return at random times. This whole sequence happened several times in a week, then stopped for good.

Now, the problem is back, with a bonus: at idle only, the actual RPM is jumping up and down, with occasional engine stops. When the engine cut, I was able to start it back up again immediately.

Anyone seen this before, and can tell me what is going on?

Thanks in advance

[carguy83]

did you get water into your intake somehow?

[sierrap615]

the first time and the second are almost definitly not related IMHO. an erratic tach reading with no accutial change in engine RPM or performance is an electrical issue. an accurate tach reading and erratic RPMs may be mechanic or electric(but not the same circiut as above).

there are many possible causes at this time, if there is a SES light, pull the codes ( http://differentracing.com/tech_articles/diag_info.html ) that will help pinpoint the problem. can you also go into more detail about when this happens? hot/cold, park/drive, highway/city driving, any special work done latey? ect.

[ESGrauer]

Problem starts while driving in lower gears (1-3). No engine work done lately, and temperature doesnt seem to make a difference.