I just rebuilt my S4 NA and got it running yesterday. I'm having some issues and I'm lost on what to do next.

Firstly, while cold, it will not idle at all and dies unless I'm on the gas. It, however, will not surge while cold. Not really wanting to start cold either.

Once warm, it'll hold a smooth (+/- 50rpm) idle. At any other steady rpm, it will want to surge +/- 250rpm.

While accelerating there's no surging and it sounds normal and very smooth.

I have a new fuel pump from mazda, fresh filters everywhere, new ngk plugs and wires, rb manifold and muffler with bonez cat, and I did remove the emissions equipment (egr, air-pump, bac, thermowax) and the "rat's nest". Everything else is stock as can be. I did bump up the idle screw a bit according to the emissions removal intsructions.

This is my first FC and my personal knowledge base is RX-8 centric. What should I try looking at or playing with to get it smoother?

 

whats your idle set at.. What kind of port? Are you sure all the emissions stuff is blocked off correctly and you dont have a vac leak. Also, it could be alternator. Check what kind of voltage you are getting at idle.

 

Start with the simple things like a properly tuned TPS. G/R wire at TPS should read 1 volt w/key to on when the car is fully warmed up.

 

Alternator is new also. It's a standard 6-port.

I did find a missing vacuum cap and replaced it. Idle went up 200 rpm and now surges like the rest of the time.

I'll check the tps sensor now, just got back from another 'test-drive'

 

Well, my brand new multi-meter is a dud. Looks like I get to wait 'til tomorrow to replace that.

 

It was the tps sensor. It was at 4.97 volts when first checked. Was able to back it out to 2.02 volts. Guess I need a new one.

Thanks everyone