Tomm1011

I have done the "IDLE RELEARN PROCEEDURE" several times. I cannot get a consistant low speed idle. However with outside temp of 38° to 47° F the idle is perfect at 550 rpm. A4 will sit still with little or no brakes on level ground. The average idle is about 750 rpm at any outside temp above 47° F.
Any suggestions where to look for wear,ect., weak sensor ect. Will be greatly appreciated.
Engine temp above 175° on all tests, does not seem to have much influence on idle. It does get a little better when it reaches 175° but only correct at 38 to 47 outside.
Thanks in advance for any clues or suggestions.

Tomm1011

Bump

enoniam

First off do you have a stock computer tune? Do you have a stock intake and MAF setup?

Tomm1011

Yes, all stock , no tune, no codes showing.

enoniam

I suspect you've got a small air or vacuum leak somewhere between the MAF and the intake valves. Computer applies idle airflow trims and it likely can't apply enough negative trim at the warmer temperatures.

Tomm1011

Thanks will give it a close going over.

Tomm1011

Thanks, will give it a close going iver between the air intake and tge throttle body.

tblu92

A vacuum leak would make it idle HIGHER than stock--not lower----
The most often issues for a lower than stock idle a=on a mostly stock engine is either the T-Body or the MAF--or both----Especially if you have a cold air intake that uses an oiled filter----The oil fouls the MAF and it will read erroneously --The latest technology is now using "oilless" air filters----2ndly your T-body should be cleaned at least once a year--Carbon build up changes the dynamics on it's efficiency---Take the entire air bridge off and open the blade and spray with brake clean or TB cleaner-same goes for the MAF----On the T-Body you will be shocked to see some of the black tar like build up--Cleaning the MAF and T-Body cleans up and restores the idle on 95% of all cars---

Tomm1011

Getting a SLOW SPEED idle is.my problem. Cold outside temps ,good. Warm outside temps, bad.
Your suggestions are all good, however. I've carefully cleaned the t body and checked and retightened all clamps and connections.
Between 34°f and 47°f the idle is perfect, 500 to 550 in gear, A4. Idle increases with outside air temp to around 750 to 800, just enough to. Be annoying at stop lights and cold traveling down a country road.
Thanks for the interest though. Will keep searching for the answer.

Bill Curlee

When the engine is COLD,, it idles off of a SET COLD IDLE TABLE.

After the engine coolant reaches operating temp and the PCM goes into closed loop, the idle is controlled by wide variety of sensors.. O2 sensor, MAF, MAP, ect... The PCM uses all those sensors to adjust idle.

SO,,, You could have a very WIDE variety of sensors that could be contributing to the issue.

??????

WHAT ENGINE.. LS1--LS6

WHAT year car???

How many miles is on the odometer???

When was the last tune up done??

Check the PCV system tubing and hoses for ROT/LEAKS?DAMAGE!!


Here are the TWO PCV Systems that you could have. BOTH are prone to causing big vacuum leaks!!!!!!!!!

LS6 Style:



LS1 Style with the problematic Y fitting t the back of the intake manifold:

Bill Curlee

Plug the openings and either pressure test the pluming OR Vacuum test the pluming. Should NOT be any leakage in any of the fittings rubber hoses or plastic tubing!!

Tomm1011

1998 LS1, 124567 miles. New PVC system including all plastic pipes and hoses, vin correct from Chevy dealer. All test were done with engine temp at or above 175°f.
On cold days 34 to 47°f the idle is very near perfect. Above 48°f the idle is 750 to 800 rpm.
A4 calls for 500 rpm in gear, little or no creap at stop lights. @750 you gotta hold the brake if you don't you're going to hit something or someone.
It's so nice to drive on cold days , I just want it to do the same when the weather warms up. Thanks Bill, you're the best

Bill Curlee

I recommend that you find someone with EFI Live or HP Tuners or purchase a scanner that has LIVE SENSOR Monitor capability and data log the sensors.

Something is NOT happy when the outside temp is above a specific deg. The sensor that comes to MIND is the Intake Air Temp Sensor. Its mounted in the AIR BRIDGE on the drivers side. See if it actually reads / matches the outside air temp at engine OFF KEY ON. Then see if it stays fairly close to Outside air temp as the engine warms up.

There NOT expensive. Hell, Just change it if your not willing or able to play. Also make sure that the connector, wiring and its FEMALE PINS are not spread apart and damaged.

If you monitor the sensor with an OHM METER it should follow temp in a SMOOTH linear increase and decrease with outside temp increase/decrease. Pay particular attention at that TRANSISITION temp where you are having issues.

Bill

Tomm1011

Thanks Bill, this is exactly what I've been looking for.
This has been my suspect all along but I do not have enough experience with the c5 programming to have a good place to start. You have given me new look at an old problem. I'll get one, repace it and post the results.

Tomm1011

outside temp 58°f
Engine temp 187 °f
Idle speed 500 rpm in drive , 600 rpm in neutral
Life is good.
This makes 6 issues CF and BC have helped me to resolve.
My sincere thanks and Best Wishes to All contributors.

Bill Curlee

SO,,,, That sensor resolved your issue? What did it read at KEY ON/ENGINE OFF?

Glad it was that simple.

Bill

Tomm1011

Another beautiful day. car wash and another test. PASSED.
Didnt check for voltage or ohms.
Your suggestion just made so much sense, and it worked, thanks again
Tom

Bill Curlee

EXCELLENT!!

BC

formvman

What is the idle relearn procedure. Mine runs slow at times