bczee

I have a problem of High Idle on my 88' TPI C4..

I had set the low idle for the IAC and set TPS.. Thought I had it fixed, but after a few days driving it around town with no problems (no highway)... but it has returned after a 30-40 mile Highway/freeway trip yesterday.

I had cleaned the MAF and Throttle Body, connections, O2 Sensor, plugs, Cap/Rotor the first time and as I stated, thought it was fixed for a few days.

What have others found or tried to resolve this (seem to be a common problem for many). Do you think the IAC motor is flaking out ?

Also seem to be hard starting at times.. Will crank and not start, afer a few attemps, it will start up if I floor the throttle and once it catches.. pedal the throttle a few time to keep it running and then it seem normal.

jsup

Did you check the injectors?

RandyJ75

Check out your Coolant Temp Sensor, it acts like a choke on a carb, you will need to have it scanned and see what it is reading.

Square

If you have recently set the base idle, I would check it again. If it is higher, then it should be caused by the IAC or a stuck throttle plate.

bczee

Thanks. I will see if I can get around to checking or re-checking those items.. The ECT is the one on the front of the Intake, right ?

After reading a lot of threads and researching, Is it my imgination or do the TPI's seem to be problematic on the High Idle and related problems ?
This is my 1st TPI car, I recently picked it you, as the last owner had it for a year, but was just driving it and really didn't know what he was doing as far a maintance and fixing things. I have since reslove all of the code that it was throwing.. (34, 36, 42). I am still learning where all of the equipement and sensor are.. I am no Newbie to car.. just the TPI..

thanks.

AGENT 86

Look for fuel in the fuel reg vac line, then test your fuel pressure and leakdown. May have a bad injector or cold start valve.
http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
http://members.shaw.ca/corvette86/Co...0View%2086.pdf
http://members.shaw.ca/corvette86/Co...rt%20Valve.pdf

bczee

Thanks for the documents.

After checking the vacuum lines and all, couldn't find any thing leaking.

On Checking the Throttle body, IAC and TPS... I found that the throttle was sticking some and that on trying to set the low idle and TPS settings.. that it seems that the IAC was not working correctly.

I had sprayed down the Throttle body for a quick clean before, but after inspecting it again.. found that the IAC port was pertty much gummed up.. I have now taken it completely apart and soaking it in a can of carb cleaner.. Not sure if I should replace the IAC, but will pick up a Gasket rebuild kit tomorrow and put it back together to see if that make any differents.

I used WinALDL to check the data and found that the ECT was sending the correct singals as well as the O2 (.451), and TPS.

For the TPS.. I was not able to get it to 0.54.. 0.55 or 0.53..! Also was not able to get it to 100% open, Only about 96%. I will adjust that later.. would you suggest grinding the arm or the T/B to get it 90 deg/100%

If I find fuel in the vacuum line of the Regulator. Is that a indication of a leaky Regulator gasket ? I need to find a fuel pressure gauge to check the rest of the system.

bczee

Well.. I rebluilt my Throttle Body as it was pertty gunked up inside and needed new gaskets anyway. I also put a new IAC Valve in. I checked some of the sensor value, (I can say that I really don't understand what all of them means).. These seem normal at Idle.
ECT = normal 195-225f
O2 = .450 v
IAC = 144 counts
TPS = .55v low, WOT = 4.96 (100.1% now!)
MAF = 23 g/s
Rich/lean = 40 counts
MAT = 147.1f
INT = 129

After resetting the Min Idle and TPS, I still have a high idle after plugging back in the IAC.

I don't have any fouled plugs, In the doc, it stated that would be a indication of a leaky injector. Question.. if I had a leaky Injector, would it also cause a high idle when the IAC is disabled/disconnected ? as I was able to set the min Idle setting to 450 ok.

So I am leaning that it is not a leaky injector for now. I still need to pickup a pressure gauge, that will be tomorrow. I will watch for a leak down.

Can anyone explain how and what circuits are involved in the IAC fuinction. as to why the high idle is there when the IAC is plugged back in and restarted !? (just trying to understand more and get some insite on resolving my problem)

I am a bit fustrated (as all seemed good after the tune up, but this problem came up after a 100 mile total round trip), but I am learning a lot thanks to you guys..

I am just pressure a bit on time, as I have two more week to get it passed the Smog test, else, DMV might charge me some more fee's.

AGENT 86

Putting your foot to the floor during cranking puts the ECM into clear flood mode. If it starts faster doing this, it's telling you that there is too much fuel. Thats why I suggested you start looking for the source of extra fuel.

As for your #'s, what was the rpm for these ?
At 800 rpm, i'm at 9 grams for MAF and 18 counts for IAC.

Dads90

Not all TPS are created equal. The Wells brand form Autozone gave me fits. Bought an AC/Delco and it solved the problem. The new IAC was put back into the box (Autozone also) and the old IAC worked fine. Point I'm making is aftermarket items sometimes aren't as good as OEM parts.

bczee

I agree with you on some of the aftermarket parts.. it is a hit or miss.. some have problem and some never have problem with off brands. Tthen again some have the same problem with OEM or AC Delco !.

Well... I was only able to pickup a pressure gauge today and do a few test.. I may have found a problem or the problem

On start up, I was only measuring 38lbs... it was going up as I hit the throttle. Still High Idle (1000+)

On shutdown to see a leak down or not. it drop to zero in about 1 to 2 seconds !... Not good I thought.

Let it warm up some more and watched the running/Idle pressure... It was steady but a bit low on idle. On shutdown.. it drop to zero again.

This time on startup.. and idling. I pulled the Vacuum from the regulator and the pressure shot up to around 48 lbs.. I thought at lease I have good full pressure from the pump. Idle jumped around a bit then was stable and a bit lower, around 800, not bad?

On restoring the vacuum.. the low/idle pressure was better around 40 lbs. and idle was steady and 700+rpms / 600 in drive. also that the leak down didn't occur !

So, my theory is that the Regualtor is faulty.. and the low idle pressure is causing the High Idle by running lean ? and causing the IAC to make the idle High !?.. (ok.. start shooting holes in my thinking !LOL) ..Ok..What do you guys think (be nice, I am a newbie to the TPI system) !

I didn't have time to run WinALDL and get any readings. I hope to do this tomorrow if not, then it will have to wait until Sat. I will also change the fuel filter.

GS4-LT1

I have never had any luck with Wells...EVER! AC/Delco always seems to be the best when it comes to these type of parts.

rick lambert

Sounds to me like you found your problem......time for a new fuel pressure regulator!

bczee

Well..lets just say I have found a problem.. I am going back and recheck everything and swap out a few more old part..

Other plans are maybe to replace the ECT, Fuel Filter, maybe a AFPR, lower Fan Switch, Flush the Radiator and lower T-Stat.

Anything else you can think of guys ?.. it does have 147+ mileage... I think the original shock are still on it.. so I don't think it was treaded very well it is 20 years of being on the road.

01spirit

Did you every resolve the high idle problem. I am having the same issues with my C4. Thanks

bczee

I think I have, I responded to your private email note..

Let me know if you have other question..