Yet Another Car Won't Idle Thread...

I'm sorry if i irritate anyone by starting this conversation again. However, I did search and, no kidding, I spent 2 hrs reading threads found with search terms "won't" & " idle".

So, here's the story: removed UIM for some maintenance and did the following

1. replaced bad primary injector
2. had secondary injectors checked/rebuilt by RC Engineering (manufacturer)
3. found some crunchy vacuum lines, so replaced all
4. replaced the UIM to engine coolant hose
5. re-plumbed the fuel per Reted's "split-supply" design
6. repaired lame solder job on CAS cable
7. re-routed CAS cable to eliminate too close proximity to spark wires
8. repaired spark wire guides and re-routed same

In addition to this top-engine work, I added a Bonez hi-flow cat, Innovate wideband, Prosport fuel pressure gauge. Just did a lot of work...

Upon first startup, I couldn't get ldle below 2000 rpm. Using starting fluid, I found a bad vacuum leak in the BAC area on the right side of the engine. With careful spraying, I isolated it to the ACV and ordered new gasket plus intake manifold check valve and UIM gasket.

That repair got me 500 rpm and further starter fluid spray has no effect. There appears to still be something up with the intake, however. Some dinking with the screw adjustments on the throttle mechanism got another 350rpm. AFR gauge says 13.8. I have confirmed that throttle plates are fully closed and the fast idle mechanism is working as designed.

Also, pulled the BAC and bench tested the solenoid; it's okay. checked the port and it doesn't leak when closed. Replaced it with new gasket and Hylomar. Disconnecting the cable from it while running doesn't affect idle speed.

I'm suspecting something messed up in intake because if I pull the small hose from the back side of the intercooler that goes into the UIM next to the throttle cable and plug it, I can get idle around 900. Soon as I unplug it, it goes back up to 1160.

Going to build the PVC Intercooler Bypass suggested in several threads to get the IC out of the way. In the mean time, I would appreciate your thoughts on where the extra air could be coming in.

Thanks!


- kel -

 

ok, hoping this gets archived because getting tired of describing how to check and adjust idle..



first thing is first, do regular maintenance of the engine and checkups:

1) use a can of carburetor cleaner and spray around the top of the engine intake manifold area, any change in idle quality indicates a vacuum leak.
2) hook up a voltmeter negative lead to negative battery terminal, positive lead to the green wire off the TPS connector while still connected.
3) with the engine fully warmed up adjust the TPS adjustment screw until your voltmeter reads as close to 1 volt as possible.
4) adjust idle RPM via the air bleed screw on the top center of the throttle body until you get the engine to idle at approximately 850 rpms. if you can't just wait until the next steps to resolve idling down/up issues.
5) hook up a timing light to the battery and L1 front coil pack, plug wire closest to the engine and zero out the timing light if it is digital/manually adjustable.
6) point the timing light at the front cover with the engine running and idling below 1000 RPMs, if the engine is not idling below 1000 skip forward.
7) if the engine is idling below 1000 RPMs you can set the base ignition timing by loosening the 10mm nut on the crank angle sensor(top of the engine driver side) and twist it until the pointer on the front cover aligns with the notch in the pulley closest to the driver side of the car on the pulley. if the engine will NOT idle below 1000 RPMs you can force the idle down by forcing the TPS adjustment cam downward by twisting it forcibly to lower the idle, once below 1000 you will hear the tone of the engine change and you can adjust timing while holding the cam closed.

if all the above has been performed and the idle is still too HIGH you can:

1) be sure that there is slack in the throttle cable to the throttle body, if not adjust the cable by loosening the outboard 12mm nut on the cable at the bracket.
2) place a flat blade screwdriver down the back of the throttle body onto the thermowax adjustment cam and press it firmly down. if the engine is warm and it idles down after pressing down on the cam then your thermowax is faulty or your engine is low on coolant and the thermowax is not able to warm up and close the cam to idle down.
3) vacuum leaks can cause idle to stick high also, but usually it will lower the idle, depending on what else is wrong with the car.
4) if all else fails check to make sure that the secondary butterfly stop is correctly set, this stop is on the top front of the throttle body, it has a small flat tip screw with 8mm nut and some silicone on it to prevent tampering(if it isn't there then someone may have tampered with it).
5) loosen the 8mm locknut and screw out the screw and see if the idle drops, adjust the screw out until the idle no longer is affected and screw it in until it just slightly raises from the lowest RPM point and tighten the locknut.

if the idle is too LOW it can be due to several things:
1) check compression, low compression can cause the idle to degrade to the point that the idle adjust screw will be ineffective.
2) if compression is above 90psi and the idle adjust screw in the center of the throttle body is ineffective, make sure there's no vacuum leaks if you avoided that step..
3) if there's no vacuum leaks, TPS has been adjusted properly, timing is set.. replace the spark plugs and wires if they are old as well as the fuel filter.
4) if all the above is ineffective, you probably have a stripped down engine with emissions removed... i won't judge you since you already did it for minimal gains so no point beating the horse. adjust the idle by screwing down the secondary butterfly adjustment mentioned that is on the front top of the throttle body until you get it stable but as low as possible, adjusting it too high with this screw will result in poor idle quality because it is not an ideal idle adjustment screw.
5) the proper way to adjust the idle on a stripped engine or one with marginal compression is to remove the throttle body and adjust the primary throttle plate stop screw on the backside bottom of the throttle body.


note these instructions are for naturally aspirated engines, turbo throttle bodies are flipped upside down so the set screws will be in different locations, the primary throttle plate set screw is at the rear top of the throttle body under the top mount intercooler.

if none of that resolves the idle issue then you have a more in depth problem to resolve with the ECU inputs/outputs, fuel system, dead leading coil, yadda yadda..

 

Karack, thank you for the detailed reply and again, sorry for the exasperation. As I mentioned, I really did read a ton of threads and here is what I know/did along your points:

1. did that first and found/fixed vac leak at the ACV which reduced idle from 2000 to 1400. Spray anywhere around the engine now does not affect the problem

2 - 3. Have standalone ECU and have adjusted TPS per manual directions

4. Forgot to mention this is a TurboII. Doesn't have air bleed adjuster

5 - 7. Timing has been checked and is spot on

1b. Cable has slack

2b. Pressing down on thermo cam has no effect. I have confirmed that fast idle mechanism is working properly

3b. I'm confident there is no leak, as I get no effect with starting fluid spray anywhere on the engine

4b - 5b. Secondary butterfly stop is set correctly


3c. have new spark plugs and wires.

4c. Engine is not stripped. I have to meet Colorado emissions test, which is the reason I began this project - with the Bonez cat.

5c. Compression should be good, as this was rebuilt by Atkins about 25k miles ago.

Have adjusted the throttle stop set screw without effect.

Have checked coils, and all 4 plugs have good fire. Fuel is supplied by Walbro 255 and pressure gauge reads 45psi - recommended by RC Engineering.

There is a small hose going from the Intercooler to the UIM just downstream of the throttle body. If I plug this hose, it idles well - 860 rpm and smooth. Un-plug the hose and idle moves up to 1100, which is low as I've been able to get it by going through the stuff listed and the threads I've read.
Since plugging said hose drops the idle, I believe the problem is air getting into the intake past the throttle plates - as in vacuum leak, but I have no idea where it would be coming in.

Hoping someone would have thoughts on where else to look.

Thanks, again!

- kel -

 

that hose goes to the bypass solenoid on the back of the UIM which iirc raises idle when an electrical load is present. sounds like the solenoid is stuck open.

 

Not this hose. This one is a direct connection from the UIM just downstream of the throttle body and plugs directly into the Intercooler. I started another thread about what this hose and what it does with picture of it and where it goes on the intercooler.

I'm familiar with the one you're referencing and have checked that valve too. It is okay..

- k -

 

i know the one and described it above, it's just not a commonly talked about solenoid or even known about. the plumbing is internal to the uim, follow it straight down from the uim port.

 

Okay, here's something new:

Reading more threads, I started to suspect the dashpot. I backed it off three turns and started the car. Idle was low and smooth (didn't have pc connected so can't say exactly what rpm was). Just as I was thinking "ah ha!", I heard a loud CLICK and then the idle smoothly increased to where it's been all along.

Can't tell what that was, but it sounded like a solenoid of some sort; it was a very distinct click followed immediately by the idle speed increase

Do you know what that would be?

Okay again. Answered my own question after I read the post you made while I was making this one. I have another engine on my garage floor and took a look at the back of the UIM; I see the solenoid you're refering to and hadn't thought about that. ANYway, I unplugged it, heard the click again and idle dropped down to where it belongs.
So, now the question becomes: what is switching it on? This is obviously the problem.


- k -

 

I see in the Haynes manual that this is the "Air Supply Valve". Reading about it now...

 

Haynes says doodly about this thing (page 131). Just how to tell if it works, not what's around energizing it (let along wtf it does)

New search in progress...

 

there's 3 idle control solenoids on the turbo, i honestly can't remember the functionality of each as they rarely ever work right even on low mile cars. that one is either turned on when the ECU sees an electrical load from the alternator signal wire, the A/C is turned on or the power steering load switch is tripped. all of which are commonly failed.

 

That makes sense. In the mean time, I searched on "Air Supply Valve" which is the name put on it in the Haynes manual. Found a thread where RotaryRocket88 says it boosts idle for the power steering. I unplugged the PS load switch and it doesn't change the ASV.
You say this commonly fails? I could swap it with the one from the engine on the floor.

Do you know if the switch in question is the two-wire one on the bottom of the PS pump, or the six-wire one on top of the assembly? Is it testable?

 

could be a positive load switch, so if the ECU is not seeing 12 or 5v from the circuit it opens the solenoid, unplugging the switch wouldn't affect the issue. read up on diagnostic test procedures of the power steering sensor/switch or simply leave the soleneoid unplugged to drop the idle,

 

Thanks millions! For now, I'll just unplug it while I setup the ECU idle and maps. I wasn't able to quickly find test procedure so I'll leave that for later. Ultimately, I want it to work correctly.

Anyway, this is by far, no question, hands down, (insert cliche of your choice here) the BEST forum on the web!

Karack, again I REALLY appreciate your time to help direct me to the source problem.

Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you,Thank you, thank you, etc....


- kel -

 

you're welcome