Really Really High idle (4000rpm)

[Terrh]

I've got a 1991 TSI AWD. Stock, a few free mods (maf, clutch switch, boost restrictor removed)... Searched around online and found all the idle threads long ago but nothing covers 4000rpm idle!

Anyways... Back in september I had gotten it to idle really well, about 1000RPM and reasonably stable. The car sat for a little bit, then one day on the way to the track it decided to not idle at all anymore.. popped the hood, OH, the idle screw is gone!
I put a big vacuum hose that I'd plugged in the hole so it would idle better, it seemed to idle pretty well - just high. (1500-1700rpm).

A week or so ago I finally got around to getting a new idle screw - I just bought a whole manifold out of another turbo car at the junkyard, the dealer was driving me nuts.

I put it in, idle wouldn't go down, seemed to be about 2700 when cold and 1700 when hot.. even with the idle screw all the way in. it was bugging me but I didn't bother fixing it since the car was still drivable and I've been busy...

Yesterday I was parked and went inside at a restaraunt.. came out, fired up the car, and WOW, 3500RPM idle wtf.. driving for 15 minutes on the way home and it didn't go down any, once it went up way higher than that even.

I unplugged the idle motor and throttle closed switch just to see if anything would change, neither seemed to affect the idle at all.. unplugged the MAF (just for kicks) the idle went down a few hundred RPM but not much.
I had some spare parts around and tried to theorize what could be causing it, removed the throttle cable just to see, didn't solve it, swapped out for a different throttle body with a different idle motor and TPS on it, also changed the MAF for a spare, changed the plug wires (needed them anyways, knew they wouldn't make it idle high). checked for vacuum leaks by eye EVERYWHERE I could think of, none, the only difference is that the car seems to run a bit smoother after changing all this, also now it idles at 4000rpm! wtf.

Anyone have any insight here? I'm going to do a pressure test on the intake tomorrow but I'm pretty sure that it isn't leaking much. I'm pretty lost. Had the car for a long time but never had any major trouble with it that I couldn't figure out before now. I don't have a logger or spare ECU to swap in.. I don't even see how the engine is physically capable of idling at 4000 rpm with the throttle 100% closed.

 

[Gary 420A RS]

check to see it doesnt end up something like a vacume line off.

 

[dets]

I don't even see how the engine is physically capable of idling at 4000 rpm with the throttle 100% closed.

it really couldn't. without all the vaccum and boost leaks that are on your car, it couldn't.



So start there first. Make sure all the lines are in good working condition fix the simple stuff first.


If its not that, we move on.


HTH

 

[tom04841]

after you put in your new idle screw, did you propperly adjust it bt grounding pin 10 on the diagnostic port, and the connector under the hood near the battery?

I had a similar problem at one point when my idle screw was MIA, but my idle was only at a high of 2500 RPMs.

I am going to lean toward a vacuum leak at or after the TB though. A leak in the intake track isn't a vacuum leak.

 

[CYrUs0k5]

I'd check the screw simmilar thing happened on my buddies car. If that doesnt work report back...

 

[ADrewzki]

This may sound stupid but I had a similar issue when I bought my car. It would idle high and just driving down the road at 60 ran the car around 4k rpm. Long story short, it was fixed when I reset the ECU by removing the ground from the battery for 10 mins.

 

[markGSX]

I'd guess a bad ISC. When my ISC went bad, the car would seemingly pick any random number to idle at (up to 4K). It's pretty embarassing stopped at a red light. I found a used one cheap and it was an easy 5 minute fix.

 

[93talonkid]

i reccomend a few choice actions here, i could take off the throttle body, and clean it with your common break cleaner, check the IAC, replace the gasket, look at the throttle cable, its common that when theyre too tight it will stick and cause your throttle to stay open. I've heard of people taking like a screwdriver or a wrench and lightly tapping the coolant line area's to free of possible buildup. hope this helps...

sean

 

[femmeDSM]

I'm with MarkGSX. Check your ISC (FYI, some places refer to it as the IAC. Same thing).

 

[oldman]

1. How much vacuum are you pulling at idle?

2. Does the throttle plate close completely at idle?

3. Did you touch the IPS, Idle position sensor?

4. Did you properly re-adjust the BISS, TPS?

5. Have you performed a leak test after any of these major operations on the intake tract?

6. Have you pulled the ecu and check for ecu leakage?

 

[Terrh]

I can tell which if you read the post and which didn't

I've replaced the throttle body, TPS and IAC with known good ones, it actually made the idle go UP. The BISS is screwed all the way in. I haven't reset the ECU yet, I'm going to do that tomorrow - but I think I found the problem and something that needs to be fixed regardless:
I don't know what the IPS is - if it's the little thing that closes

I did an intake manifold pressure test today and it looks like my intake manifold to head gasket is destroyed, when I used my compressor to blow air in there it came out at a gale force onto myhand when I put it there.

it has alot of vacuum at 4000rpm, it'd be pretty impossible for it not to

but if I put the car in gear and idle down the road, and use the brakes to force the engine down to 1000rpm, there is no vacuum at all hardly, like 2".

I haven't checked the ECU for leakage - I think my first action should be to replace the intake manifold gasket, before I go tearing into an ecu when there is now definatly something that I know is wrong.

How hard is it to change the gasket with the engine in the car? Are any special tools required for this or no (I've got sockets and wrenches and etc...

 

[oldman]

Yes, a destroyed intake manifold gasket will do it. I suggest spraying down everything between your TB and head, shaft seals, BISS o-ring, injector seals, never assume you only have one leak because it rarely is the case, fix all leaks in one shot then retest from turbo inlet.

How hard is it to change the gasket with the engine in the car? Are any special tools required for this or no (I've got sockets and wrenches and etc...

What you will need is a short 12mm gear wrench, unbolt your downpipe from o2 so you can move it out of the way to get to the bottom manifold bolts from underneath.

 

[femmeDSM]

I've replaced the throttle body, TPS and IAC with known good ones

oops, missed that. Sorry. My bad

 

[Terrh]

ok, ordered a new intake manifold gasket.. thanks everyone!

I'm going to check around the base of each injector and etc for leaks too but the "spray" test didn't seem to get me very far, I could spray as much as I wanted without affecting the idle at all.

 

[oldman]

ok, ordered a new intake manifold gasket.. thanks everyone!

I'm going to check around the base of each injector and etc for leaks too but the "spray" test didn't seem to get me very far, I could spray as much as I wanted without affecting the idle at all.

I was talking about spraying soapy water on the seals during a boost leak test so you will see bubbles if there are leaks, what were you talking about?

 

[Terrh]

ohh, I thought you meant the spray-flammable-fluid-on-stuff-while-its-idling-to-see-if-it-smooths-out test.

I guess I can try that, its really difficult to see down there though with all the crap in the way (100% stock emmissions stuff).

I picked up the intake manifold gasket allready - it is definatly leaking from there on the passanger side, I thought it could possibly be the injector but the air isn't even in that area.

I asked about the lower injector grommet while I was at the parts store, they didn't have them in stock and couldn't get them for 2-3 days so I figure I'll just replace the intake manifold gasket tomorrow anyways, I really can't stand a car that goes 55mph down the road by itself...

I've got a 3" exhaust to put on the car so while I have the downpipe off I may as well put my new exhaust on, looks like tomorrow will be a busy day.
I picked up a 12mm stubby ratcheting wrench while I was out too - it should come in handy on my rx7 as well...

wow, the edit feature on this forum rocks
Is there a FSM online for these cars somewhere? I'd love to see a blow-up picture of this area... I have a spare intake manifold so I have an idea but I'd like to see how the injectors attach to the head.

 

[oldman]

I have a spare intake manifold so I have an idea but I'd like to see how the injectors attach to the head.

You don't need to remove the intake manifold again to change the injector seals so you are fine there, the fuel rail is bolted to the head via 3 bolts that the throttle cable is also bolted to. Remember, the leak test isn't complete until it's able to hold 20psi and allowing no less than 30 sec. before bleeding down to zero.

 

[femmeDSM]

Is there a FSM online for these cars somewhere? I'd love to see a blow-up picture of this area... I have a spare intake manifold so I have an idea but I'd like to see how the injectors attach to the head.

I have the Chrysler FSM if you'd like to see what it says about the intake mani. and fuel injection system. But if you are just interested in knowing how the injectors attach to the head, I can tell you that in detail without the need of the FSM -- it is quite simple and straightforward.

The injectors are attached to the fuel rail which is secured to the engine by three (long) bolts (14mm I believe, could be wrong). Each intake port on the cyl. head has an opening for each fuel injector. The bottom (metal part) of each injector rests inside the intake port and is sealed by the lower O-ring on each injector. There's really not much more to it, unless you want to get into how the ECU handles injector firing, and how the fuel gets to the fuel rail. it's all a very simple process, though; cars are only machines, remember

I hope I read your post correctly. If I told you something that was completely unrelated to what you actually wanted to know, please tell me and I will clarify. .

 

[oldman]

(14mm I believe, could be wrong).

12mm.

 

[femmeDSM]

12mm.

Ah, damn. Haha. Thanks

 

[Terrh]

you guys have been pretty helpful, thanks!

you went a little off topic there femmeDSM - but thanks

I actually know a reasonable amount about cars - just not these ones - I mess with mazda rx7's all the time but I got a talon because its AWD and good in snow - which is like 6 months of the year here.

 

[femmeDSM]

you went a little off topic there femmeDSM - but thanks

That's what happens when you get me started on anything even remotely related to the fuel system. .
Hope I helped a little, though

 

[steve]

Is there a FSM online for these cars somewhere? I'd love to see a blow-up picture of this area.

There is some stuff on the Manual CD site

Steve

 

[Terrh]

Just posting as to What Fixed My Problem, since I guess that helps out alot on search eh?


I replaced the intake manifold to head gasket and the problem, she is gone! Car drives much better and is even faster now. What a pain in the ass it was to do! but it's done. And I'm happy. Yay

 

[femmeDSM]

Just posting as to What Fixed My Problem, since I guess that helps out alot on search eh?


I replaced the intake manifold to head gasket and the problem, she is gone! Car drives much better and is even faster now. What a pain in the ass it was to do! but it's done. And I'm happy. Yay

Good times. Always good to see your hard work pay off Congrats on a running DSM Glad it wasn't something expensive. Haha.