I have had my RX-7 for 4 years, it has been one of the most trouble-free cars I have ever owned. Of course, after learning how to iron the little quirks that every 7 owner has to deal with occasionally,such as the infrequent flooding etc.
During the warmer month's of the year, I have no problems just starting and driving the car. However, when it's real cool in the mornings, 45F or below, I start the car and it does it's usual 2000rpm rev then assumes a normal idle. After a few seconds, the idle starts to fluctuate from 750 to 1500 revs. If I try to rev the car, it stops at 1500, and acts like it's not getting any fuel. As the car warms, it allows the rpm's to increase until it has reached normal temp, and then it will not rev over 3000. I have messed around with the harness that runs from the passenger side, behind the water pump, and it will stop restricting the revs after a little tweaking of the harness. Good, now I can go! Get down the road, and it does it again. I have to go up a long mountain pass to get to town, and it usually does it about 1/2 way up and I have to pull off (provided I have enough momentum to find a "safe place" to pull off) and mess with the harness again. I can always drive the Miata, but sometimes I don't want to. I have replaced the temp sensor on the back of the water pump, which will make the car have similar symptoms, and also looked at the wiring when I had the plenum off to replace the PD. Everything looked fine! Why would it only do it when the ambiant temperature is cool? Like I said, it NEVER does this when it's relatively warm outside, and for most of the year, I forget about it. Makes me want to break something!
Anyone have any ideas? or similar problems? Any help or advice would be greatly appreciated. Also, I have talked to two people I know, that are basically wizard's at troubleshooting problems w/ the FC 13B, and they don't know either.

 

Wild guess: Condentation in the harness?

 

Condensation? Well, I have not driven the car in the rain for month's. Also, I have never sprayed the engine off either. It has done this for two year's, in the winter, off and on. Sometimes it doesn't do it, but that's only about 20% of the time. I have started it on cold mornings, and it acted up, so I drove the other car. Come home in the evening, starts right up and drives perfect. I would think it would do it during warm weather at least a couple of time's, but it doesn't. Could it have anything to do with the "cold start" system?

 

thats very weird. sounds like more of a ignition problem to me.

 

I agree, it is very weird. It's hard to put your finger on a problem that isn't consistent.

 

lol this sounds ohh so familiar to me. lol I would get stuck on the side of the road.

its like when you press the gas the car chokes and dies or either almost dies?
and when you drive the car will jerk and buck right?

what I did to fix this issue was that I changed my TPS and made sure that the AFM plunger is pushed in all the way. also cleaned the contacts on the plunger and the afm with a Q tip and rubbing alcohol.

 

Condensation is created from cold temps to hot temps. When your windows are full of condensation, Ièm sure its not because you sprayed the interior of your car or because it rained inside.

Like a beer that you take out of the fridge. Its gets all wet all over.

Ièm just pulling **** out of my *** now...But I have seen condensation problems before that created problems like no starts, bad idling, missfiring and such. But mostly on american cars though.

 

Damn it! It's totally a pain in my ***. You will be driving, and all of the sudden....no power. The car never dies, or really bucks. Its almost like flipping a toggle switch, and the car coasts to a stop. I'll put the spare TPS I have on it and see if that helps. Also, was your problem "temperature sensitive"? or did it do it whenever?

 

It would only happen when it would rain like non stop. but after the TPS change the car has been running really great it hasn't rained like crazy yet..... well I will find out with this test of rain coming this winter.

as for the temp issue my does act up when it is Freezing cold, it doesn't really rev at 3k on cold start like 2.5.

 

Anyone else have any ideas?

 

Does it ver do it when you are hammering on the car? And will act like its backfiring really bad? Perhaps you have a bad ground wire?

 

No, Its either running fine, or completely cuts out. there's really no in between.

Say its a "cold" morning, start the car, may idle perfect, start down the road, run it all the way to redline if I want. then, after driving a few minutes, it may cut out completely. It doesnt buck, jump, backfire, anything. Its like someone reaches over and turns the key off, except when I mash in the clutch, the car remains running and sounds fine. Mash the gas, and it chokes at about 2000prms,more or less depending on how warm the engine is, then resumes idleing. When its real cold, the rpms will go up and down between 750 and 1500, once its slightly warm the idle stays steady. Once I pull over and fiddle with the harness, and test rev the car to make sure its going to run again, it runs like a raped ape. It may not do it again, or I may have to pull over two more times. "warm weather" no issue!

 

You've owned some piles haven't you? Lol I kid, I kid.

 

Very few, and not for long! No kidding, this car has more that exceeded my initial expectations. I have put 65,000K it since I owned it, and have not been stranded one time that I actually had to walk. Ive replaced the PD, ball joint, drive shaft u-joints, new exhaust, one hose and one belt. I have owned 17 autos in 12 years.

I can list them if you want, you might be surprised!
EDIT: This is my third FC

 

Condensation does seem like a good guess. On the hottest, driest day, there is still water in the air. When it gets cold (even if there's not a cloud in the sky), it leaves the air and settles on everything.

I'd check your wire insulation on the harness. A multimeter to check for conductivity and resistance might be handy too. Something might be getting disconnected or might be poorly connected.

 

Thanks, I'll check it out.