90Camaro4ever

iTrader: (2)

My 3.1 starts and idles at 750-800 rpm after a few minutes. When I give it gas, the car reacts as expected. I do not have any codes. I also have a scanner, but nothing seems unusual. After driving for 10-15 minutes, when I come to a stop, the idle stays around 1200, sometimes 1500 rpm. If I am cruzin at 60 (1600 rpm), and I let of the gas, the rpms stay at 1600 and would go for miles on level ground.

With the car stopped after a run, if I disconnect the MAP sensor, the idle drops to 800. If I stop and the car is at 1200-1500 rpm and I rev the engine once, the idle will slowly drop to 800.

I have looked at the throttle linkage and at the intake and nothing appears to be stuck or sticking.

Any ideas as to why the vacuum is staying high and keeping the rpm up? I have sprayed carb cleaner around the vacuum lines and intake gaskets and no increase in rpm was detected.

Help!

RBob

iTrader: (1)

You can check a couple of items with the scan tool.

Once warmed up and it is idling high, check the IAC counts (steps). If they are zero that is a sign of either a vacuum leak or a bad IAC. They should be in the 30 - 40 step range at idle.

Before kicking the idle down, look at the TPS% value. It needs to be lower then 1.6% (for the AZTY calibration). A high TPS% is a sign that the TB is sticking and the ECM won't even try to idle down. It thinks the driver has the foot on the gas pedal.

Check that CTS value. Make sure that it is in the proper range for the engine temperature (about 200 F).

RBob.

90Camaro4ever

iTrader: (2)

Thanks RBob. I was able to take if for a spin today while having the scan tool connected. I have all 42 values, but I will list the ones I think are appropriate.

While driving 70mph, Coolant temp was 172 (start temp was 45); rmp was 1925; ESC counter 17; IAC was 44;Idle req 800; inj pulse 3.4; MAF 93; MAP 2.31; MAT 23;O2 sensor 790; O2 cross cnts 169;runtime 17min; Spark adv 37; throttle 12% TPS sensor volts 1.18; closed loop;

When driving on the highway, when I removed my foot from the gas pedal, the throttle went to 2%. Every time I stopped and the throttle was 2%, the car did not idle down as expected, the idle stayed up around 1300rpm. Like you said, the ECM must think I was accelerating.

Only once, when I cam to a stop was the throttle position a 1%, and that time, the idle dropped as expected.

When I stopped and the car was idling high, I also recorded the following values: Coolant temp was 180; rmp was 1300; ESC counter 17; IAC was 0; Idle req 863; inj pulse 1.5; MAF 21; MAP 1.18; MAT 30; O2 sensor 977; O2 cross cnts 203;runtime 25min; Spark adv 37; throttle 2%; TPS sensor volt .82; closed loop;

So I noticed the IAC counts were at 0. But I am kinda confused now. I was thinking if the rpm was calling for 863 and the actual was 1300, that the IAC count would go to zero to reduce the air and lower the rpm.

But with the throttle at 2%, why would the IAC move at all if the ECM thinks I am accelerating the car. HELP!

So I did spray the outside of the TB linkage with WD-40, but I am not sure that is really going to help. Does any one know what their TPS % is when they let off the gas when the engine is running? Should it be 0%? Any suggestions on how I can get mine to 0%?

With the above readings, does anyone think my IAC is bad? I just put a new one in 3 weeks ago because I was receiving a code 35.

Thanks!

RBob

iTrader: (1)

I would tackle the high TPS% first. Usually what causes this is that the throttle shaft bores on the TB egg out. Which in turn causes the throttle blades to hang open a little. If you can find a lower mileage TB, or get the current one re-bushed, or add another spring to help close them.

It may also be that the TPS is bad. But by being able to 'kick' the idle down I am more inclined to look into the TB shaft bores egging out.

If you can do PROM burning another way to go is to raise the minimum required TPS% to go into idle mode. This works too.

For the one time the IAC was at 0 and the idle was high. It may be that the ECM is learning in a lower IAC setting due to the throttle blades hanging open a little, but not so much that the TPS% is too high.

The ECM learns in the 0% TPS value by retaining the lowest seen TPS value. That value becomes 0% TPS.

RBob.

90Camaro4ever

iTrader: (2)

WD-40 did help. TPS was showing 2% before wash, and 1 % after wash. I believe the real problem was the way I tightened the throttle linkage screws (2) after I replaced to bad injectors. After the WD 40 bath, I loosened and re tightened both screws, and I could tell they moved to a different more aligned position.


Now, every time the tps position shows zero when my foot is not on the gas! Thanks for your help. The car goes to idle when I stop. No more high rpms

I reset the computer this afternoon, and want to see if my codes and IAC counts get off of zero. I will keep you posted.

RBob

iTrader: (1)

Cool, good to hear that it worked out. If you have an auto trans (700R4) you should do an idle learn after the ECM reset. An idle learn with a stick trans is simplier and usually works out on it's own.

RBob.

90Camaro4ever

iTrader: (2)

I read the Tech Article today (and before) about the IAC adjustment. I was always confused by the wording because I seem to think after 20 minutes, the ECM will learn on its own. What am I missing?

I also read previously that you should not attempt to start the engine when A-B is jumped. Doesn't every ECM output turn on when A-B are shorted? How could the engine run well enough to idle down to 450 rpm and not stall? Or is the procedure missing a step to disconnect the A-B jumper?

Am I supposed to disconnect the IAC with A-B shorted? and Key on?

The procedure does not tell you when to disconnect the jumper.

Is the procedure implying that every time the IAC is replaced, that you should set the min air to 450 rmp with the IAC disconnected? Using the procedure above?

Could you share how you perform this procedure with me?

RBob

iTrader: (1)

The procedure you are referencing is for setting the minimum air. For that the easiest is to check a scan tool and get the IAC at 30 - 35 steps in park/neutral and no load. Otherwise I wouldn't mess with it.

Here are a couple of links to the idle learn and some other info:

https://www.thirdgen.org/forums/v6/1...procedure.html
https://www.thirdgen.org/forums/v6/1...dle-learn.html

With the '7730 and $88 mask you can short A & B after the engine is running. The ECM will then use the SES light to blink out rich or lean as reported by the O2 sensor.

A 10K resistor between A & B puts the ECM into diagnostic mode. All kinds of things change in this mode.

RBob.

90Camaro4ever

iTrader: (2)

Thanks for the info!