High Idle searched to no avail

[Zardoz]

Ok, I've been searching through threads since yesterday and have found some that sound close to my problem and tried the solutions presented but still no dice.

Here's the car:

• 1997 Eagle Talon ESi (420A NT)
• My son and I rebuilt the engine about a year ago (got a lot of useful info from this site, Thank You!)
• New Old Stock crankshaft
• Bored .5mm over
• Speedpro Hypereutectic pistons
• Cylinder head rebuilt by a professional shop (stock cams and valves)
• Stainless Steel exhaust from header to tail pipe (one of those ebay specials)
• Plus all the usual suspects when doing a rebuld

Here's the problem:

• Car ran great for a long time (months and thousands of miles) then started idling high.
• From a cold start it idles at around 2000 rpm then quickly ramps up to around 2800 rpm and maintains 2800 rpm idle while warm.
• When the throttle is "blipped" it responds crisply then drops into the 1500 rpm range very briefly before returning to 2800 rpm.

Here's what I've done so far:

• Capped each vacuum port in turn to determine if a vacuum leak in any of those systems might be the cause. No changes to idle speed.
• Checked MAP ignition on engine off against barometric pressure and was correct.
• Checked MAP at idle against vacuum gauge and was correct.
• Vacuum at 2800 rpm was about 18 in-Hg (I didn't think to write it down, that's from memory). Sounds good to me, any thoughts?
• I replaced the TPS after throttle response was not linear, fixed that problem but idle still high.
• I tried hooking the old TPS up to the connector and started the car to see if maybe the throttle shaft was holding it "open" but there was no change in idle speed. I left the new TPS in place to avoid a vacuum leak.
• TPS Voltage with throttle closed 0.8v and at WOT was 3.93v. (according to what I've read on here the voltages are high)
• Checked resistance from TPS connector center wire to pin 35 at ECU, 0 ohms and no ground (short).
• TPS connector disconnected, ignition on, engine off, top wire reads 5.0v, middle (signal wire) reads 4.8v, bottom wire reads 0.01v.
• I cleaned the IAC (aka ISC) and still idling high.
• Checked the resistance readings on the IAC according to the Haynes manual, readings were a little out of spec.
• Replaced IAC, still idling high.
• Checked plugs, clean with no signs of over heating or fouling.
• Plug wires: 1 - 2390 ohms, 2 - 1950 ohms, 3- 1730 ohms, 4 - 2490 ohms.

Anyone have any ideas? Why is the TPS signal voltage 0.8v when from what I've read here people are getting 0.4v to 0.6v? And what can I do about it?

 

[slickers111]

How open is the throttle?
I had this same problem. It turned out to be that the previous owner had the cable pulled too far on the throttle body. I just moved it up a little, and she Idles at 1100 in park, and 850 in drive.

 

[Eton]

check how far to the left the plate that tightens throttle cable, it should be just a little snug. you could just have the throttle a little open so its messin with your idle

 

[GreenDemon95]

You might have an intake leak. Listen around the sealing points of the intake or put some sea foam in the vacuum port. You may want to check your throttle screw also.

 

[Zardoz]

Hey, thanks for the quick replies!

There is just a slight bit of slack in the throttle cable and the throttle does seems to be shutting completely. When I had the throttle body off I cleaned it and verified that the throttle was smooth and returned to a closed position.

I'll check for leaks in the intake. I read in another thread someone had the o-rings on two of their injectors tear while installing them and that caused similar symptoms. So, I'll check those as well.

I'll update later and let you know what I find.

Thanks again!

 

[chiuchimu]

If the idle is consistently high from cols start to warm up and doesn't go up and down, then its an intake leak. First check hoses. If they are new or not leaking then its from a gasket somewhere. If the rpm slowly got higher and its slowly getting worse then it means bolts are loosening and more and more air is leaking from the gasket. To check, spray water or carb cleaner around possible leak locations. If there is a leak, the engine rpm will go down. You have to do this while engines cold because once really warm, the water or carb cleaner will evaporate before even hitting the engine. also, carb cleaner is flammable, so don't shoot it at anything really hot or a spark source.

 

[Zardoz]

Cool idea! I'll try that tomorrow.

 

[Rob10_99]

Intake manifold or TB gasket most likely, did the gasket tear when you took off the TB?

I would just do a boost leak test on the end of the TB and that should show where its leaking, no problem.

Did you reuse any of your gaskets when you put it all back together? Egr, or intake maby?

 

[Zardoz]

To check, spray water or carb cleaner around possible leak locations. If there is a leak, the engine rpm will go down.

That worked like a charm! As soon as I hit the passenger side of the intake with some water it slowed down.

I took it apart this weekend and the gasket just crumbled. I can't remember the brand I ended up with for the intake gasket when I did the rebuild, it was nearly a year ago. I'll have to see if I can find it in my receipts...I wanna stay away from that brand from now on.

It's all back together now and running great! Idles at about 950-975 rpm!