Jory

ok guys 1st post here, although i have read an awful lot of useful info on this site I am finally desperate enough to post lol. I have a 85 z31 NA auto which I have constantly been rebuilding over the past few years. For the past few years it has been having trouble starting and staying running, if it doesn't die right away the idle will fluctuate lower and lower draining power visibly each time until it dies. Idle is fairly rough at stoplights until warmed up. Over the past 3 years I've been to 4 different mechanics, had a tune up, starter, cold air temp sensor replaced, idle air control replaced and most recently a new engine among other things.... nothing worked until i disassembled the air intake and cleaned the throttle (which was COVERED in black soot). Put everything back together started up 1st try and roared to life... i was ecstatic!!! Now this morning i go to start up and same problem, trouble starting but idle was still noticeably better at stop lights but the fluctuation was still there barely. Any idea with my persistent starting issue? I know my way around but I'm not a mechanic... any help would be greatly appreciated... and if there's anyone from dallas willing to help that would be even better :-)

NismoPick

Welcome to ZDriver!

Start with checking the ecu diagnostic codes.

Jory

yeah, did that I'm getting the code for throttle/idle air control which is why i cleaned my throttle body out

rogerz

here is some stuff to do that may help out.
Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen.

Clean the connectors for the maf or afm, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion.

vacuum leaks are the bane of an FI engine. try the unlit propane torch trick to locate if you have any.

CHTS can be a problem for some of what you describe. download the fsm from xenon and look at what the gizmos do that control idle. have you checked your fuel pressure?

Jory

out of all that the only thing i haven't done is checking fuel pressure or vacuum leaks. It's a new battery, good connections, CHTS was replaced, MAF is only a couple years old and still looks clean. I have the FSM thank god, that thing is a godsend. How do i check fuel pressure and what is the propane torch trick, i haven't heard that....

rogerz

put a pressure gage between the filter and the fuel ring. You did change the fuel filter? get a handheld propane torch. open valve. don't light. spray propane around the engine. if it revs up quite likely sucking in the propane thus providing extra fuel to the engine. the z31 ground strap should be grounded behind the battery to the frame with a bolt M8 i believe. Don't put a lot of faith in the diagnostic codes they have seldom if ever helped me out.