Having a strange idle issue
 

Have been having some idle issue with my R1. It starts fine and never stalls, however, after reaching full operating temperature idle starts to vary. It does not hunt or anything, just from time to time it would idle at 900 rpm than switch over to 1300 rpm. A lot of time it spends in the 1300 rpm zone.

A couple things that I've noticed is that when it switches over to a different idle speed i can actually here some kind of clicking in the engine bay, sounds like around the throttle body area.
Another thing is that when it idles at 900 rpm afr's go into 11.5 and when it switches over to 1300 rpm idle the afr's lean out all the way to 17-18 afr.

Other than that the car feels and drive great. Also, pretty much a stock car except 3" downpipe/midpipe and silicone vacuum lines.

Any suggestions highly appreciated

Start with pulling and cleaning the ISC. It's on the back side of the intake manifold, you can probably remove it without pulling the upper intake manifold. 1 plug and 2 10mm nuts hold it on.

Clean it out with brake/carb cleaner, lube it with WD-40, and use 2 jumper wires to click it back and forth and work the piston a bit.

Start with that then go from there.

Dale

It may be caused by the cooling fans coming on which causes a higher idle speed.

I will be doing this soon aswell. can you point me in a cleaner direction a picture perhaps
thanks dale

Here is a link I found with a lot of pictures:

Banzai Racing FD Block-Off Plates Location

thanks man . did cleaning the ISC help your idle ?

is your heater/defrost on when the rpms go higher?

with the PFC on mine if I turn on the AC (even with out the ac compressor installed) it will raise the idle quite a ways ( thinking a load is coming)and kick on the fans

if you don't have air conditioning, then it will obviously overshoot, thinking the a/c compressor is putting a huge load on the engine.

OP can you clarify your mods:

Has there been anything deleted from the engine such as the air pump, throttlebody coolant hose, A/C or power steering? Are you on stock ECU? Do you have the stock thermoswitch or not? Is this the original engine or rebuilt? ported?

What accessories are you running when you are looking at the idle? What does the idle do when you start the car?


Here's a test. Cold start the engine, cranking in 1st gear with all accessories off. Then let it sit there until the temperature gauge gets to the middle. Then flip the A/C on, then flip it off. En flip the lights on, then flip off. Record the idle speed at each one of these points.

It should be around 1500rpm cold start, then drop to about 700-750 when warm. Then there should be a slight bump with accessories on, including the fans coming on when it gets warm enough. So when you say you are at 900rpm it's important for us to understand what the accessory load and temperature condition is.

Hey guys, thanks for all responses so far. Unfortunately, I haven't had the chance to remove and clean the isc yet as suggested by Dale but it's definitely on my list of things to do. I have too many old cars and sometimes they all need work done at the same time :rolleyes:

But to answer some questions, the car in question was a bone stock R1 with 80k miles on original engine. Shortly after I bought the car I replaced all vacuum lines, eliminated FPD, and built a 3" exhaust from turbo to catback. Also, installed the wideband.

The air pump, a/c and everything else is still hooked up and working.

When I cold start the car in 1st gear, it idles at 1500 rpm than after it warms up a little but not all the way it goes to 900 rpm and idles at 14.7 afr. Only after it reaches full operating temperature it starts idling at 11.5 afr @ 900 rpm or 17.5 afr @1300 rpm.

It never idles at 750 rpm and turning on load like a/c compressor or headlights doesn't seem to affect idle.

Would an out of adjustment throttle cause this? I think not but wanted to ask anyway.

A throttle cable that's too tight can bump the idle up a bit. It's physically cracking the throttle open. This is pretty uncommon, though.

Also, idle AFR's with a wideband and an airpump are going to be off. The airpump is injecting air which messes with the wideband reading. With an airpump the only time you can trust the reading is at WOT or high RPM.

Any time you have a high idle it's going to be air getting in when it shouldn't. You need air to set the idle. Vacuum leak, sticking ISC, something will cause it.

Dale

Check the free play of the throttle and cruise control cables, if equipped. There should be a little bit of slack in them (I think 1-3 mm was a spec I read in the service manual). After cleaning the ISC valve and checking for vacuum leaks, first thing I would do is wait for the 1300rpm problem to occur again.

When the idle bumps to 1300, it could be a stuck fast idle cam, which basically opens the throttle plates when the engine is cold and closes them by the movement of the hot wax rod. The hot wax rod is operated by the throttlebody coolant hose.

https://www.rx7club.com/attachments/...adjustment.jpg

You can rotate the fast idle cam with your finger. If you rotate it and the idle comes down, then there could be some sticking.

There is an idle setting procedure in the service manual, but don't mess with that until you've done the above checks (throttle/cruise cable, vacuum leak check, fast idle check). Be careful about adjusting screws on the throttlebody though, because you may just be bandaiding some other problem like a vacuum leak.

Is the ISC referred to the same thing as the idle air control valve? Elsewhere a bench test was described for the IAC valve using a 9v battery.