I have not had much time to check things out but I did check the brake booster. It's holding vacuum so that's not the culprit.

The subject vehicle is a 96 LT1. It has OBDII, unlike any other previous year C4. The high idle condition has not set off any check engine light as of yet.

If set at 800 by the tuner, and it's idling over 1000, and such high idle is cause by a vacuum leak, that would be a pretty significant vacuum leak wouldn't it?

 

See if your cruise control works just replace my hose was like a nasty black night crawler

 

It's hard to diagnose without ever seeing the car. Just have to recheck everything done during the cam swap.

A quick, no tools way to check the idle air control: start the car, remove the brake booster line from the intake, don't completely remove it just let it idle high for 20-30 seconds then put it back on. It should idle down with the hose put back on. It would probably stall if you did this and didn't have a high idle problem. If no change it might be the IAC.

You could also take the throttle body off and look at the idle air control pintle. It should be very close to seated if it has a vacuum leak somewhere. If it's not then the problem might be the IAC itself.

What about the back of the intake manifold, is the air tube connected properly, no cracks in the piping? Gasket ok? EGR on properly? Intake gaskets look straight and even from what you can see? Throttle body gasket not upside down?

As a last resort and easy check just disconnect and plug everything connected to the intake manifold. If it still idles high you can rule out all the external vacuum accessories.

You sure the rubber seal is properly installed on the MAP sensor?

 

Yes i've seen cab inside line is in good condition, i didnt remove panel, however thought removing it should be easy to reach nipple

 

let me know it was not on my 94

 

Yep

Will let you know as soon as possible

 

In my opinion idle should return at 900 rpm always, both engaging neutral or pressing clutch pedal... If this not happen a clutch slip occur, so I thought that is not a good thing, a wear in clutch bearing can happen

 

Air tube gasket is good. I never removed the throttle body, egr, map sensor from the intake during the cam swap. I didn't disassemble anything that I could leave together. All sensors that could remain installed were not removed. I just lifted the intake with everything intact and put it back the same way. There were no idle problems prior to the cam swap.

I did the brake boost hose remove test. The idle didn't change much when removing the hose partially simulating a smaller leak. Even completely removed, simulating a larger leak, it still idles about 1100 but roughly. When I put the hose back, it idled down in response. If I put it back gradually, it would idle down slightly before coming back to 1100. If I put the hose back suddenly, it idled way down and stalled out. So I guess this mean the IAC if functioning correctly and I can rule it out?

Intake gaskets are in as they should be as far as I can tell. It seems like if I had a problem with them, symptoms would be more dramatic. Other than high idle, the car runs great and again, no CEL.

I used a propane torch (unlit of course) and spilled propane all around the top of the engine focusing on the intake runner to head area and TB gasket area. No changes in idle during this test.

Maybe I can expand on symptoms and spark other ideas. As you know I mentioned high idle at 1100. Furthermore, when cruising along at 45-50 for example, take foot completely off gas and the car keeps going as if you still have your foot in it. With 3.54 gears, the thing should surely slow down some, even with an 1100 idle. At this point, the momentum seems to be much greater than a simple 1100 rpm idle would do. Is it possible that there is an issue with ASR making it behave like the cruise control is on when its not?

I'm going to pull the IAC and check it for buildup. Then I'll drive it with the ASR turned off and see if there's a difference. Although, when at high idle in park the throttle bracket is all the back against the stop. That's already been verified.

 

So, cruising along in OD at 40mph reving 1500rpm. Put it in neutral and take the foot off the gas to coast, continues to rev 1500 as if the vehicle speed is influencing the engine speed, even with the trans in neutral. Should it be doing this?

I did clean the IAC pintle and it brougth the curb idle to 950 in park, 800 in gear while stopped.

 

Is your cruise control messing up try unhooking it

 

Hello

I would pass you my experience of today ...

I've drained all coolant.. And flush block removing knock sensor, then replace them,

Since that i've removed intake hose, i've spent some time to check IAC and TPS torx screws, well they were no tight so i've tighten them, and now idle is improved, thought that now it is properly working, also TB bolts need to be tight

 

I now have an OBD II scanner that can live stream all perimeters and store data for printout. Before I do anything else, I'm going to check that to see if anything looks abnormal. If it all checks out as normal, I'm going to close the throttle blades and let the IAC take over full control of the idle and see what happens.

 

Scan data in attached PDF. There are 10 frames. The scanned indicated a DTC of bank 2 #1 O2 sensor not active. I cleared it so we'll see if it comes back. It has not triggered the CEL. The scanner reported idle speed is about 1000 rpm lower than the idle reported by the tach in the dash. At 1500 rpm, they are the same. So, can you detect any issues with the data in the PDF?

 

Yes it was, i would figurate that in your car vacuum switch nipple is ponting up. Sinche that in my car they can rotate

 

Good job mine was pointing up a real pita

 

TB cleaning seems to have helped.

 

Absolutely PITA Mmine too, even if a visible nipple is, there's no room to work, i've done it with fingers only

 

I was going to go back and ask if you looked at the earlier suggestion to give us the idle IAC Counts to see if the car was even able to control the idle. I have had to drill TB blades to get the IAC to be in the range to control the idle.

However you have split BLMs so you have other problems. You need to find out why one side is running way rich and the other is not. You seem to have worked hard on a vacuum leak, so now need to go to the fuel side of the equation. But you need to get the left and right banks in some kind of reasonable comparable FA ratio before you do anything else. You gave us static O2 sensor readings, but are they both (only worry about the ones in front of the cat) moving around in about the same range (random movements from 100 to 750)? I just had a dead/lazy O2 sensor cause me to fail a smog test. Very easy to diagnose and test simply by looking at the split BLMs and then watching the O2 sensor readings in real time.

 

Don't drill throttle blades to try to correct split blm's. Drill the TB hole that feeds through the intake to each individual port.

 

When you replaced your cruise control vacuum hose, do you remember if those three switches were thighten or easily rotating?