Tach RPM fluctuations
Asked by skyteam Dec 07, 2009 at 04:44 PM about the 2003 Saturn L300
Question type: Maintenance & Repair
My veh. (totally equipped)81,000km Just replaced the MAF after my eng light ON. Since this time my RPM's fluctuate especially in warm weather. When I stop/go, the RPM's go up(normal) but when I stop(rev down to 250 ) and then rpm's level off like a yo-yo effect. This only happens at low speed(ie: traffic bumper to bumper, stop and go)Dealer is unable to locate source. ECM reprogrammed and throttle cleaned, EGR cleaned up out and still problem persists. All help appreciated to eradicate this problem.
4 Answers
MAP or IACV, Manifold Air Pressure sensor may be bad and telling the Idle Air Control Valve (which may be bad too) to stay open which would cause the high RPMs
Thanks for the reply, much appreciated however you mention my Rpm's are too high. This is not the problem. It rev's up normally as any car should. The problem is when I let the gas go, it rev's down to such a low RPM and then jumps back up to normal levels. The yo yo effect makes the car almost stall. In fact today approaching various STOP signs, I let the gas go and the RPM's dropped to a point that the engine stalled. 4 alarm bells rang but not a single dash warning light lit up indicating a malfunction ! I really need HELP on this issue !~
If this is really an L300, then it has the V6 which is a fly-by-wire design which means a servo motor actuates the throttle, not a cable. This engine does not have an IAC valve, nor does it need one since the PCM can adjust idle by opening or closing the throttle slightly on its own. The culprit is usually a dirty throttle body not letting sufficient air through during idle. When the engine dips low on RPMs, the PCM compensates by opening up the throttle more which causes it to overshoot. It then compensates by closing the throttle down to the idle position which starves the engine for air causing it to almost stall. This causes the PCM to compensate yet again which creates this never ending yoyo effect. Get some throttle body cleaner and clean it well. If you can remove the throttle body and clean it off of the engine even better.
I have one more and its kind of a question would a loose oil cap do this? to but mine does it while driving and idling. And if so how long until it goes back to normal?
