Backfires and odd idle issues
 

So it's been awhile since I've been able to work on the RX-7 but now that I've got a bit of free time I wanted to start clearing up some of the issues I've been having.

Backfires. Almost every time without fail I get backfires ranging from small pops to really loud, horrible sounding backfires. The really bad ones usually come from when I'm in first gear and pulling out of a parking space or something similar. When I take my foot off the gas pedal it almost sounds like the engine cuts off entirely, waits a second or two, then BANG. Immediately after the backfire the engine almost sputters to come back to life. The smaller ones are while shifting gears or idling. These backfire only occur when the car is cold, once warmed the up the backfire cease entirely.

The second issue I'm having is with the idle. This issue is, once again, only when the engine is cold. The idle will sometimes sit around 2k and will level out some if I tap the gas pedal. It can also be very low at times and has always been a bit twitchy, bouncing very slightly between 950-1000 RPMs, even when hot.

My third issue(?) is with the check engine light. If the keys are in the on position(car is off) the light will stay on. When I turn the car on, the light will turn off, but having it stay on with the keys in makes me think something is wrong. I've tried checking for codes but it always comes out clean.

Any help in resolving these issues is greatly appreciated.

-Jon

The check engine light SHOULD be on when the key is in the on position and the engine is not running. The cold idle is either a vacuum leak of a TPS out of adjustment. A TPS out of adjustment can also cause the popping in the exhaust. Does your car still have ALL emissions equipment?

Might have forgotten that part, sorry about that. No, the car is current running a RB header > straight pipe > catback. The TPS could be out of whack and I'll check it later tonight. Would the lack of a cat/presilencer create the backfires/idle issues?

His car is an S5.
For Future reference Please put in your thread the series of car or guys are just going to Guess what your problem is.S4 and s5 are slightly different.

Sorry about the lack of information, let me give a bit of detail. 1990 vert s5, 32k on rebuilt motor, cone air filter, new(8months) spark plugs, new TPS(done at time of engine rebuild), RB header/pip/cat back, everything else is stock to my knowledge.

Check the timing, it sounds like its set a bit to over. Start and warm your car, then loosen the bolt (10mm) that holds the timing thingy tight. And turn it just a bit clockwise.
I think this is the prob cause it sounds like your burning fuel faster than it enters the chamber when you decelerate.

Just got back from checking the timing, both at cold and warmed up it is dead on the mark.

Have you checked your tps adjustment and connection? If it's not turning on or way out of adjustment it will cause backfire.

Also check for vacuum leaks.

The TPS(narrow range) should be set to 1v with the engine hot if you still have the cold idle thermowax, if you don't have it just set it to 1volt cold.