Alright, first of all let me apologize to all my forefathers who taught me better. I have a 1988 300 SEL 92,000 miles that recently had the CEL come on. Car was running okay except for RPM oscillations (500-800) and rough idle at stop signs and not a lot of power. I have read quite a few threads on both the CEL and rough idle. Have a CA car and the diagnostic code was #4 which I understand to be the air flow potentiometer. Anyway, thought i'd check out some of the simple stuff first. Changed cap, rotor, and plugs. Cleaned up the ICV, throttle linkage, and microswitch. Thought I would take off the OVP and shake it to see if it "rattled". Had a little trouble getting it off. . . used a screwdriver. ....accidently touched a pin or two and heard a couple clicks. Replaced OVP, started car, and so far nothing is wrong. OVP fuse is ok. Car seems to be running a little better, still with rough idle, but no RPM variations at rest. The odd part is that the CEL is now off and when I check the code it gives me #1 for no codes. My question is, what if anything could I break by shorting the OVP? Is it possible that I shorted the ECU and that is why the CEL went out? If everything seems to be running fine, should I just ignore the pop/click I heard? Last of all, how specific are the CA diagnostic codes. Is it possible that with my simple fixes I corrected whatever was making the CEL come on and I won't have to replace the pot?
Any thoughts would be appreciated.

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Eric Zacharias

'88 300 SEL
'64 Ford Falcon
'99 Infiniti QX4

Day #2 and still driving ok. Anyone know what the overprotection relay protects?

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Eric Zacharias

'88 300 SEL
'64 Ford Falcon
'99 Infiniti QX4

Do a search its been explained numerous times. HINT: Its a glorified surge protector.

I have read as many OVP posts as my poor little eyeballs could withstand. It is not clear to me yet whether the OVP in a 1988 300 SEL protects the KE jetronic system or just the ECU. As my AC seems to work just fine I assume that my ECU is ok. What I don't know is if that means the KE is ok. Car is running well but my understanding is that if all the mechanical is in good working order, the loss of the computer might not be readily apparent.

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Eric Zacharias

'88 300 SEL
'64 Ford Falcon
'99 Infiniti QX4

Try this thread.....don't mind Steve.....he had a heavy day !
http://www.peachparts.com/shopforum/showthread.php?t=45977&highlight=ovpr



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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

That thread was very helpful. I appreciate your sending it my way. I will check the duty cycles tomorrow.

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Eric Zacharias

'88 300 SEL
'64 Ford Falcon
'99 Infiniti QX4