1990 1.6l with intermittent power and idle issues

[Andrew]

Hello everyone, first post here and i figured id give it a shot!

I have a 1990 Stock 1.6L Miata. I have been driving the car for a while without any major problems but a few weeks ago, i put lucas fuel injector cleaner in the tank. No problems ocurred but instead i actually had improvements in acceleration.


Last week when it started to get really cold here, i started the car up and it didnt idle high like it should on a cold start, instead it idles at about 1200 RPM. When i gave it gas, it would stumble/hesitate and also the exhaust had a deeper louder tone also it would backfire. When i would go to accelerate, it wouldnt backfire at all, but there was barely any power at all and it the acceleration seemed to come and go as the RPM increased. After the car would warm up and be driven for a while, the power would return like there wasnt any problem.


When the power returned i had accelerated to about 6k and came to a stop. when i took it out of gear, the RPM dropped fairly quickly and below idle then back up to idle and then the power was gone again. later on after driving carefully the power came back again.


I should also note that when i didnt have power, i could pres the A/C button and the RPM would only go up to 1.2k instead of the normal ~2k and drop while idling rough.


The car has new NGK plugs and wires. Also when i had the car running, i pulled the plugs one at a time and they all were firing. I cleaned the throttle body a while back but neglected to clean the IAC and ever since then i havent had a set idle of 850 and leads me to believe it got TB cleaner down in it gunking it up a bit and have been thinking that maybe thats the culprit? since the low temperatures and such.

Any help is appreciated! I hope this is enough information to narrow down the problem. I dont believe its a bad keyway on the crank since this comes and goes as the car warms up.

Thanks in advance!
-Andrew

[OZMDD]

Sounds like you've fouled something, though cold temp swill affect your idle anyway. You might want to take a good look at your cooling system/thermostat/water temps/fans while all this is happening. If the engine isn't warming to proper temps, it will try to idle high. Check the heat range on your plugs too. Could be weak coils, exhaust leak, etc.

If the car never idled poorly before, you need to back-up and determine what made it change. Even in cold weather, the car will behave about the same at idle once its all warmed up. The injector cleaner is unlikely to have changed anything, for better or worse, in that short time.

[Robert]

I would start with the fuel filter, sometime when you put in a cleaner it will break lose the gunk in the gas tank and plug the filter. Even if that is not the problem, it probably needs it anyways.

[OZMDD]

Good point.