Surging Idle????

[Yeats5.0]

I have already posted once that I'm having this issue, but I have done the vacuum check with a smoke machine - no problems found. Gone to the TSRM site and done the voltage test and ohms test on the ICV and the TPS - no problems found.

Heres what I did find out though: the min air screw in the throttle body has been messed with. It was turned out 3-4 turns, but when I screwed it all the way in the car would not idle. I turned it back out 2 turns and acheived the idle I wanted - took a test drive and then began to work on wrapping up a boost gauge install. I fired it up to go for another drive and it was back to the 1500 to 900 up and down repeatedly again. I also noticed the ICV doesn't have coolant being supplied to it any more, someone must have elected not to use that anymore. Can that affect it? I also unplugged the TPS and fired it up and it revved up to 2300 and stayed there? I'm starting to get frustrated. I don't like replacing parts just to rule them out. I like to prove a fault. Any thoughts?

 

[jdub]

Did you pull the ECU codes?

The TB screw should be all the way in...did the engine die when you did it?

The coolant line to the ISCV is there to prevent icing issues. It is a factor at high humidity and low OAT.

 

[Yeats5.0]

No on pulling codes. Yes, when I screwed in the TB screw it died and would not restart unless I gave it throttle, then it would die when I let off.

 

[jdub]

Pull the codes. Then clear the codes by pulling the ECU fuse in the engine bay box for a minute. Start the car and screw the TB screw all the way in again. Recheck the codes after you've run the car.

Do you have the stock PCV system installed?

 

[ATL88Supra]

sounds more like your idle control valve is not working, if i am right it works as a bypass from the throttle body to actively control the idle, i hear that sometimes they get stopped up. when i cleaned mine the mesh was full of carbon and gunk.

 

[Yeats5.0]

No, it is just 5/8" heater hose from the tb to the valve covers to the accordian intake tube> i will pull codes in a few minutes

 

[Yeats5.0]

Ok, it has a 41 and a 34. I just put on the turbo and I did not have a boost gauge that worked on it. I drove it and it boost pretty hard and hit fuel cut - could that be the 34?. I also started it earlier with the tps unplugged, 41?

 

[Yeats5.0]

The check valve is missing in the end of the ICV

 

[ATL88Supra]

may want to get that check valve then

 

[Yeats5.0]

I cleared the codes then refired the car. The idle surging is now faster but the same RPMS. The codes were gone until I hit the throttle - now has a 51. Something with the A/C? Don't really care about A/C

 

[jdub]

The check valve is under the ISCV...looks like a little mag wheel. It's there to prevent boost from reversing flow through the ISCV routing...if missing, it should not affect idle. You do need it though

Is your ISCV routed the same as stock, to the accordion hose?

Code 51 will occur anytime the AC button is pressed or the TB plate is moved from idle position. Normal because you hit the gas pedal.

Code 34 is fuel cut...it should clear when you pull the EFI fuse.

Code 41 is the TPS or the wiring to it...when you unplugged the TPS earlier, it probably induced it.

Did you screw the TB screw all the way in like I said (after the ECU reset)? What happened?

 

[Yeats5.0]

Yes it is in all the way now - really no change. Codes are gone except for the 51 every time I hit the gas. The ICV hose goes to the accordian hose just like factory. Earlier today when I adjusted that screw on the TB in, the idle came down. At least for a little while. Now it is still doing the same thing.

 

[jdub]

Like I said, that's normal for a code 51. Tells me the TPS is working and adjusted correctly

Ok...leave the TB screw all the way in.

Pinch off/block the ISCV hose and PCV hose to the TB (motor running)...you don't want any air flow through either. Tell me what happens.

 

[Yeats5.0]

That check valve might fix the squeeking sound I hear under boost:icon_bigg

 

[Yeats5.0]

no idle

 

[ATL88Supra]

it wont matter if your ISCV is busted.

 

[jdub]

No idle...you mean the engine died when you pinched off both hoses?

 

[Yeats5.0]

The ISCV is not broke. Its just missing the check valve. The operation of it checks out perfect - all curcuits ohm correctly and the motor moves in and out just like it should.

 

[Yeats5.0]

I pinched off both hoses then tried to fire it up. I have to give it throttle to start and it will not stay running. I'm trying to keep this diag as quiet as possible. When it is running up and down it is very loud.:naughty:

 

[jdub]

Ok...that pretty much rules out vac leaks. I know you checked with a smoke machine (and I believed you), but this confirms it. The engine should die.

Check the accordion hose for any leaks/tears.

Confirm the ISCV opens on engine shut down. It should hear it click or feel it with your hand on the ISCV motor.

ATL88's suggestion earlier is next. Pull the ISCV and clean it. You will have to remove the 3 screws securing the motor...be careful with the round gasket.