Idle still sucks

[guy48065]

I replaced my IAC 2 days ago and now that the re-learn honeymoon is over my car is behaving exactly as it was $169 ago. To be precise--the idle is rough and causes a lot of engine movement which visibly shakes the car. Once hot it often doesn't quickly idle down when I coast to a stop and even slowly surges to 2500+ RPM. NOT fun in stop & go traffic. Car behaves pretty normally for the first 30 minutes of use--it gets worse after the engine has soaked awhile at normal running temp. Idle speed is fairly constant at 650 according to the tach--but I'm sure if I could view it on a faster meter it would be erratic. Or not--maybe it's missing. Oh yeah--the only code I've ever gotten was a high idle code.

Prior to the IAC I replaced the TPS. No effect.
Cleaned the EGR. It wasn't blocked or even crusty but I wanted to do something with it. No change.
New plugs. Stretched plug boot springs. Cleaned & greased everything good.

These are all the suggestions I've read here and now that I think about it most threads never get closure with a "That Did It!" so there might be a lot of us chasing our tails.

What else could it be??

I recently learned of cellphone scanner apps & cheap bluetooth adapters. Would I learn anything from using one of these or is the data hard to interpret? I had a laptop scan program back in the Windows95 days but never really knew what to do with the info it showed me.

[wickhamizer]

I'm gonna run down a whole list of things that the manual suggests checking for rough idle. First, check PCV valve. As you already replaced the TPS, I'll skip that step. Check the knock system for excessive spark retard. I'll skip EGR and IAC. Inspect for dirty intake and collapsed intake hose. Moving on to the fuel system, check fuel pressure. Also check fuel injectors and related wiring. Test for contaminated fuel. Inspect the following that may cause the engine to run rich:

•Any water intrusion in the HO2S connector.
•Engine oil contaminated by fuel.
•An EVAP canister purge condition.
•Incorrect fuel pressure—Refer to Fuel System Diagnosis.
•A leaking fuel pressure regulator.
•Any rich fuel injectors—Refer to Fuel Injector Balance Test with Tech 2 and Fuel Injector Balance Test with Special Tool.
•Inaccurate MAF sensor— Refer to Scan Tool Data List.
•Blockage on the inlet screen of the MAF sensor.
•Vacuum hoses for splits, kinks and proper connections.
•The air intake duct for being collapsed or restricted.
•The air filter for being dirty or restricted—Refer to Air Cleaner Element Replacement.
Inspect the following that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices.

•Any water intrusion into the HO2S connector.
•An exhaust leak between the HO2S and the engine—Refer to Exhaust Leakage in Engine Exhaust.
•Any vacuum leaks.
•Incorrect fuel pressure—Refer to Fuel System Diagnosis.
•Any lean fuel injectors—Refer to Fuel Injector Balance Test with Tech 2 and Fuel Injector Balance Test with Special Tool.
•An inaccurate mass air flow (MAF) sensor— Refer to Scan Tool Data List.
•Fuel Contamination—Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
•Vacuum hoses for splits, kinks and proper connections.

Ignition System
•Inspect the ignition control (IC) circuits for proper connections at each ignition module assembly.
•Test for proper ignition voltage output using the J 26792 Spark Tester.
•Inspect the ignition coils for cracks, or damage.
•Inspect for a missing or damaged ignition module assembly grounding spring.
•Inspect for misaligned, or damaged spark plug boots.
•Inspect the spark plugs. Refer to Spark Plug Inspection.

Engine Mechanical
•Inspect for the following:
– Engine compression—Refer to Engine Compression Test in Engine Mechanical.
– Sticking or leaking valves
– Worn camshaft lobes
– Valve timing
– Worn rocker arms—Refer to Valve Rocker Arm Cleaning and Inspection in Engine Mechanical–4.0L.
– Broken or weak valve springs—Refer to Valve Spring Inspection and Measurement in Engine Mechanical–4.0L.
– Excessive oil in the combustion chamber-leaking valve seals
•Inspect for incorrect basic engine parts. Inspect the following:
– Camshafts
– Cylinder heads
– Pistons, etc.

Additional
Inspect the exhaust system for possible restrictions. Refer to Restricted Exhaust in Engine Exhaust.

[guy48065]

Long list--but everything that isn't affected by heat can be ruled out since the car idles smooth and steady for the first 20-30 minutes.
The high idle seems to point to something within the control of the ECM since it never does it cold while open loop. I'm thinking it's something ignition related but there may be more than one fault causing the rough idle and the runaway (high) idle.

[wickhamizer]

Yes, it is a long list. The best thing to do, in my experience, is to just start at the top and work your way down until you find what is broken or the problem goes away. Often I get blessed and it is something simple and easy, but sometime it is not. Have you checked to see if there are any codes stored? They often give you guidance on where to start looking for the problem.  I just reread the origional post and saw you had a high idle code.  Do you remember the number?  It could help narrow down the list of things to check.

[guy48065]

Can the camshaft sensor cause my heat- related, intermittent idle problems?
Can someone post a link to the thread with replacement instructions? I get a "not found" from the sticky and an error when I try to search for it.

Meanwhile I have ordered the bluetooth OBD2 adapter and will see if I can learn anything from the data available.

[canaboy]

I suppose you had the throttle body / MAF sensor cleaned out ?? And you also cleaned the seat in the throttle body when changing the IAC ?

[guy48065]

Yes.

[guy48065]

Well the OBD2 data is a bust. Not enough channels in the 2003 GM implementation to view camshaft and crankshaft sensors so I still don't know if that's the issue.
It's starting to look like my local Cadillac dealer is my only hope.

[canaboy]

Not sure about the cam sensor, but the crank sensor can cause high/ rough idle. You would need a code reader / scanner to tell which crank sensor is not working. Usually it is the one behind the starter motor. I had it replaced twice----result of using cheap parts I guess.

I did not see you mention if the check engine lite is on or off...........

[guy48065]

See my previous post. I didn't find crank (or cam) sensor parameters on my scanner. Don't know if that's limitation of the ECM or my scanner (Torque for android).
I get a high idle code only.

[tennesseerip]

I had a high idle problem with a warm engine and it was a vacuum leak in the rubber connector between the mass air sensor and intake manifold. If you haven't checked, check for vacuum leaks and also the throttle position sensor can cause accelerated idling.

[bufo]

My wife's 2003 Aurora also suffered from a rough idle earlier this year. It slowly got worse and then there was a noticeable general loss of power.

The problem turned out to be a misfiring cylinder caused by a bad ignition coil. Replacing the coil fixed the problem. Spark plugs were replaced too. Running smooth now!

[plato442]

Aug 11, 2014 21:05:12 GMT -6 guy48065 said:

It's starting to look like my local Cadillac dealer is my only hope.

guy48065, what did you find out?

[guy48065]

aurorah.proboards.com/thread/28774/hello?page=2

The Caddy dealer wanted over $900 to replace the "plenum gasket" and told me it only comes with a new plenum. I think they made a mistake and priced the replacement of the intake rather than the intake boot.

Did it myself for about $25. Running good now and getting 2mpg more than before.