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Originally Posted by Gilly
Yeah lots of things can blow that fuse. Jumpstarting is a biggie
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Ok. Lots of cold start cranking and jumpstarts last winter likely did that. See below.
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In regards to if it's been blown for awhile, one big indicator is how well it ran when cold, as the car is designed to run well when WARM if that fuse is blown, but runs cruddy when cold, hard to start and keep running. Also the idle control valve is in a fixed mode w/o the OVP fuse, but normally will idle.
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My reply may be rather long to cover all the ground...apologies for taking up your time.
Gotcha though as per fried fuse = helll to start all winter - but once it warmed up no problem, ran/runs smooth. So yes you're reply tells me that fuse was shot ages ago. ~But~, surprise surprise, I just took the fuse out of the OVP just now as I mentioned I would above in my reply yesterday, and got my 200 RPMs back! (running/limping)
Problem not solved (truly) but my car is back the way it was for the last two yrs I've driven it. I can live with it since it's always been this way. I would however like to get to the bottom of the low idle and get it all working just right because I intend to sell it and get my better condition 300E that I recently purchased on the road in a month or so.
Anyhow.,...
Without the OVP fuse I have my RPMs back, I can turn everything on and there is no worse lowering of RPMs due to power being taken away from that circuit. The downside if I leave it like this, there will be hard cold starts again.
But it's back to "normal" as far as me being used to 600RPM at idle once warmed up, no more near stalls at every red light or in traffic and with summer now close - I've got more time to sort the low idle problem out. I use the car daily and driving around worrying about a stall every stoplight or turned corner was a bit too much on the nerves. Removing fuse as an experiment clears one whole side of the problem up. It's not the FPR or the OVP or the fuel pump. So now I move onto your suggestions below.
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In regards to no idiot lights on but the OVP fuse maybe was blown, it sort of depends on the car. BIG question is if any of the idiot lights in question would come on when you turned the key to the "on" position. If they didn't, it may have some blown bulbs??? Usually the indicators are SRS and ABS.
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Always come on when ignition first turned on, bulbs are there. - never came or come on while running. Why is a mystery still. Two working fused or OVPs gave similar results, good starts but low idle RPM. No idgit lights come on after car starts with _or_ w/o fuse. Only light I've ever seen come on at the outset of this repair was the "check engine" light, which comes on when the O2 sensor isn't right (apparently). My car wouldn't pass an emissions test this year for my plate sticker so I know there are issues in the exhaust system. As an aside, in Canada, $500 bucks buys a "smoker" car a "conditional pass". If anyone can explain to me how that leads to a cleaner environment please make me the first one to know. Only in Canada eh?
Anyway, that Check Engine light only came on one or two times when we first fired up after repairing the FPR solder connection - and hasn't returned since. It was likely unrelated, or the lousy catalytic converter smoked up with a rich fuel mixture after repair and there was not enough O2 present for that short period. It hasn't come on since FPR repair two weeks ago.
While I'm here on that subject anyway, I might add that a duty cycle test shows that engine running on the rich side. Gas mileage isn't the greatest either. The guy testing said all other readings are right so any adjustment would throw the right ones off for me to get a leaner mixture. Six of one - half dozen of the other, so we didn't adjust the cycle with the allen wrench.
Summary. Runs rich with or w/o fuse in OVP. No idgit lights come on with or w/o that fuse. Engine runs with low RPMs (4/500) with fuse, normal 6/700 spec idle RPM without fuse.
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Try this, start the car, warmed up engine, pull the connector off the idle control valve and see if the idle changes, and if not can you hear the valve clicking. If you hear nothing, check for power on those 2 wires going in to the idle valve, one should have 12v power, the other is a ground wire, which is controlled by...oh hell, either the ECM or a seperate idle speed controller, forget which now. The power is coming from the OVP. If no power is there, the OVP you installed might be "close but not close enough".
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Since I tried two, now three different (working fine in other 88 300Es)
OVPs ending up with similar lower idle RPM results - could it not only be that the idle control valve needs replacing? I do not hear anything since the engine is a little noisy running and I'm not sure, having never heard the sound, what to listen for exactly. I'll pull the connector tomorrow in daylight and see if idle changes but assume I'd have to put fuse back in OVP for that test?
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As an aside, you can just jump power to the fuel pump using 2 existing connectors at the FPR socket, no need to buy a FPR just to diagnose. You can just use a jumper wire as a test. You can't leave it like that though as it is not switched, the pump will run contantly. You can DRIVE it like that, but not a "repair". Just to test or to get the car home or to a shop.
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Yep, we did some of that on our first pass with the FPR that had the bad solder connection. We jump tested which told us that the FPR was faulty and it was the reason for the total breakdown initially because what remained on contact on the bad solder finally let go and all power to fuel pump quit. That's now behind us. FP and FPR works great.
The car runs fine as I said above but it would be nice to nail down what is really causing the low idle so I can put the fuse back in the OVP and get those easy starts in the morning again.
Hoping whatever is causing the problem, whether idle control valve or other control, is also causing it to run rich as well. Likely wishful thinking but if this tells you anything, in that a faulty idle control valve also results in a poor lean/rich mixture, do let me know.
Again ... thanks a lot for your time... what a great resource having some guys with experience at the other end of this computer.