1995 Cobra - high cold start idle, flashing CEL, miss/hesitation/low power when driving

02 281 GT

Agreed...My wife has great Boobs
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I've been having an issue with my '95 Cobra that started a few weeks ago. After driving in a heavy downpour with partially-flooded streets (may be irrelevant, but figured it's worth mentioning), the car started to experience a surge in idle to about 2400-2500 RPM with a flashing CEL almost immediately (withing about ten seconds) after a cold start. It's not a hunting or "surging" idle. The idle will go up to the mentioned RPM and will remain very steady while the CEL flashes. It will return to normal idle and the CEL will stop flashing after a minute or two. So far I have not experienced this after a warm/hot start. It's behaving almost as if the computer is entering a KOER test mode.

Aside from this, it's also been experiencing a miss/hesitation/low power while driving. This will occur in any gear at any speed between part and full throttle and is seemingly random. When it happens, the car will buck and the engine seems unable to rev higher than 3000 RPM.

The problem seems very similar to the one that joetrainer31 posted about a few years ago here, with the exception that I have no TPS or IAC codes. I also ran an SCT chip for a while, but I removed it about two years ago.

I pulled codes with the following results:
KOEO: 327 (EGR feedback signal low), 552 (AIR solenoid/circuit failure), 553 (AIR solenoid/circuit failure), and 558 (EGR vacuum regulator solenoid/circuit failure).
KOER: 311 (Thermactor system inoperative, right O2 sensor), 314 (Thermactor system inoperative, left O2 sensor), and 327 (EGR feedback signal low).

The EGR and smog systems were removed from my car about ten years ago. I have considered reinstalling the EGR, but haven't gotten around to it. I'll have to purchase new components or junkyard parts since my originals are long gone.

I haven't yet checked TPS voltage. I need to buy a multimeter first.
 
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jozsefsz

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Most of those codes probably don't mean much. Your symptoms (bucking / surging) sound like possibly a lean condition.
The high water situation might have damaged the MAF (if you sucked water into it), maybe damaged the O2 sensors (if they got doused with some cold water while they were red hot or soaked the connectors), both of which could cause some problems with your mixture.

I'd start with checking the fuel pressure. I'd also go through the 'Surging Idle Checklist' sticky to make sure your IAC, idle air bleeds, and throttle stop were all set properly. Then it wouldn't hurt to check MAF basic voltages (TPS as well if you're so inclined). And if the O2's were up there in age I'd consider changing them. But it's going to be a bit of a mystery without some datalogging - so these suggestions (minus the O2's which you could consider routine maintenance if they're 20 years old) are largely free at least.

The O2's are used to determine if the thermactor is pumping air into the exhaust, and it's not detecting that extra air. Which is understandable with the AIR system removed. However, at idle, that shouldn't be much of a factor as the air pump isn't putting out too much volume even if it were present. Which is why I'd suggest the O2's may be suspect.
 

02 281 GT

Agreed...My wife has great Boobs
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It took a while to get to with school work and such, but I got the new Motorcraft O2 sensors in today. The driver's side put up a fight, but a MAP torch make quick work of that.

The surging idle on start up appears to be gone. Not only that, it starts up and idles extra smooth—at least it seems so. The O2 sensors on there were not Motorcraft, and I seem to recall reading something recently that the factory sensors are better than aftermarket versions. Whatever the case, I'm glad that's fixed.

The missing/hesitation at part throttle is still there. I may have a dead spot in the TPS. I need to buy a multimeter before I can test that theory. Hopefully that won't take another two months. It probably will.
 

jozsefsz

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That's never a bad thing to check. It may also take some time for the computer to re-learn fuel trims with the new O2 sensors. Hopefully it'll start to improve as things are re-learned. If you didn't, it may not be a bad idea to disconnect battery for ~30 minutes to reset the computer. It'll then re-learn everything as new - it may run a bit crappy for the first several trips after you do this.
 

02 281 GT

Agreed...My wife has great Boobs
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Problem is fixed.

I did the computer disconnect and it ran the same. I decided to try troubleshooting some of the spark and fuel components to see if I could find the culprit. I started off by swapping the ignition coil from the Mercury since it uses the same coil as the Mustang. Problem solved. I put an MSD coil on the car shortly after I bought the car ten years ago.

Now that I think about it, the miss/sputter problem had been there for several years. It was just very seldom that it would happen. Every couple of months you would be on the highway and it would feel like the engine would sputter for a split second and then recover. It wasn't until recently that the problem started getting really bad. Anyway, the Mercury's coil is in the Cobra for now and a new Motorcraft coil is on the way.
 

jozsefsz

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My MSD TFI coil started leaking and causing spark blow-out at boost about 2 years into its lifespan, so it's good you got that many years out of it. $50 and an Accel Super-Coil later and the car's never run better. IMHO MSD is pretty-looking Chinese junk - their coils that leak, their caps that fit sloppily, and their wires that arc right out of the distributor-side boots.
 
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