SR Idle Problem

[Fahaka]

I have and SR that will not idle.

I performed the swap about a year ago, and have searched all forums for a possible solution.

I will first start with the basics.

The car is an '89 automatic coupe.
I swapped the ka and auto transmission for a '94 blacktop and 5 speed transmission.
I replaced the t25 with a gt2871r.
other mods include:
650cc injectors
FMIC
300zx mafs
3" turbo back exhaust
BikiRom daughter board tuned by CG tuning.

With the stock sr mafs, injectors and ecu the car would not idle. Specifically when the motor is started it will rev up to ~1500 rpm and then drop down to 750 with a bad misfire and then die. Above 1500 rpm the car is fine and runs quite well.

I swapped the sr mafs for a sohc mafs, with the same result. I tried another brand new sohc mafs and it still did not fix the problem.

I sprayed an entire can of carburetor cleaner into the idle air control valve in an attempt to free up a possible stuck valve with no change in idle.

Once we changed to the 300zx mafs, 650cc injectors and bikirom tuned daughter board the car would still act the same way (For the record I was not expecting a change, but I was hoping that this would do something). Still above idle the car ran well and made good power (See also no traction in first or second gear at 20 psi).

In November, due to a faulty actuator I cracked a ring land and decided to remove the motor and rebuild. I machined the block installed cp pistons with eagle rods new bearings freeze plugs, head gasket etc, and while I had the motor out and the manifold off I changed the idle air control valve for a known working used one hoping this would fix the persistent idle problem. It did not.

I have now installed a known working ecu, still no change.
Swapped harnesses with a known working harness, no change.
Replaced all rubber fuel lines in case one had an unseen leak, no change.
reinstalled stock injectors, sohc mafs and stock sr injectors, still no change.

Today I worked a sold 12 hours on this car attempting to get it to idle properly in order to pass emissions here in AZ with no effect

I have run out of possible solutions with the exception of replacing the iacv with a brand new unit.

If any SR experts who have encountered a similar persistent idle problem could chime in on this subject I would greatly appreciate it.

Also when I disconnect the mafs the car idles fine.

[fliprayzin240sx]

Vacuum leak? Make a tester and push compressed air into the whole setup and check for leaks. If not that, check sparks. What sparkplugs and gapped to what. Also double check the timing...verify that you are at 15 degrees.

[Fahaka]

Vacuum leak? Make a tester and push compressed air into the whole setup and check for leaks.

I have not checked for a vacuum/boost leak. All of the rubber lines to and from the manifold are new, and there appears to be no boost leak under pressure.

If not that, check sparks. What sparkplugs and gapped to what.

Spark plugs are properly gapped.

Also double check the timing...verify that you are at 15 degrees.

I can't set the timing very accurately because the car won't idle.

[fliprayzin240sx]

Do a search in google for a home made vacuum/leak tester. You can make it from stuff from Home depot. Once you make one, connect it into your intake piping and connect an air compressor on it. Make sure you crank it down to maybe 20 psi tops. Listen for noise, you will hear leaks. If that checks out, again, what spark plugs are you running and gapped to what? I want to eliminate that if possible.

When you check your timing, play with the TPS plug. Try it on and off and see if your idle settles when you try to shoot it.

[Fahaka]

The plugs are ngk's gapped to .028 Edit: correction they are gapped to .28 not .028...

when the tps is disconnected it has no effect on the idle.

When I disconnect the mafs it idles perfectly, but then it just sucks above 2k...obviously.

[s13gold]

There might be a leak in intercooler piping under boost, even a small leak will make the car buck while opening up the throttle. hence not idling correctly.

or have someone else wire up the maf for you. just in case ur messing something up.

hope this helps, this is alll i can think of since the iacv valve has been cleaned thoroughly and the plugs are gapped to spec.

[chrisman2k]

You got a leak some where. If not, your sensor isn't wired right, but to check for leaks, here ya are

Go to a hardware store, buy some PVC pipe ends that fit the rubber inlet fitting of your turbo, a male air hose fitting, some teflon tape.

Drill hole for fitting and assemble

Pull off intake pipe, put ghetto made leak tester in place and tighten down.

Set air compressor regulator to 15psi BEFORE hooking it up to ghetto tester

Hook up air hose and listen for leaks

It may take a few seconds for the system to fill and stabalize, but thats it. I have made several of these and it works perfect!

Oh, screw the smog in maricopa county, find a friend or sombody in gilla county (ie. payson) like me and have no smog at all. I live in cali and when I get pulled over, this is what I say "no smog required"