1996 LeSabre - high idle when in gear

1996 Buick LeSabre
3800 (not super charged)
Mass Air sensor was replaced a couple weeks ago which solved rough idle/occassional stalling issue.
Car starts easily in all conditions
110,000 miles

Here are my observances, please bear with me:

1.
When engine is cold and started it initially idles high and drops to normal idle all within 30-60 seconds.

2.
When driving it drives normally but when coming to a stop (stop sign/red light) the engine is still revving high and will not drop to a normal RPM until you put it in park or neutral.

3.
If you come to a stop and did not put it in neutral or park and simply take you foot off the brake the car will idle up to a speed of 25-30mph.

4.
When the engine is at normal RPM the idle does not increase by simply putting it in gear, the increased RPM only occurs after driving and coming to a stop.

The car runs and operates normally in all other areas.

Thanks for reading.

Welcome to AF! Check for a sticking T/B or TPS out of range. You can look at both on a scanner. This may also be a leaking power brake booster.

Welcome to AF! Check for a sticking T/B or TPS out of range.

I apologize but I am not exactly sure what a "T/B" is. All I can come up with is Throttle Body, am I correct?

This may also be a leaking power brake booster.

This may be related; when my foot is on the brake and it is idling high while in gear, the brake feel changes when I put it in neutral. :rolleyes:

I went to Autozone and had the codes pulled for it today, I also replaced the air filter and put in some fuel injector cleaner (Placebo at best, I suppose).

Here are the codes:
P0171
P0102


P1870 <-- I believe this one has to do with a selenoid in the transmission. I believe there is a service bullitin for it.

P0107 indicates the 02 sensor has detected a lean condition on bank one. Look for vacuum (air) leak downstream of the MAF sensor.

P0102 is for MAF malfunction. Did you remove the DTC's after replacing the MAF sensor? Clear all DTC's and see what comes back!

BTW, T/B is for the throttle body. Sorry about that.

No, the codes were not cleared. I thought the guy would have cleared them after reading them yesterday, but he did'nt.

Correct me if I am wrong, I can clear the codes by removing both battery cables and touching them together? I read that someplace yesterday but it IS the internet whch means it is full of disinformation.

Just disconnect the negative battery cable for about 10 minutes. Touching the battery cables together,to reset the DTC, is not necessary and is internet misinformation, and it sounds dumb.

If this is a 96 as the OP listed, it is OBDII and disconnecting the battery cables will not clear the DTC's. Take it back to AZ and ask them to do it!

Just a side note to clearing codes.

My 2001 cleared the codes on its own. I don't know if this works with a 96 Lesabre but mine just eventually cleared itself.

The computer must have had some sort of self-clearing system. It took less than a week for it to self clear but it did.

Maybe you might want to wait a few days and see if yours does as well? Your choice. Beats paying to have the codes cleared at a garage.

Update:

I made a long trip a week ago, about 1000 expressway miles, and averaged 20mpg which, from what I understand, is quite low for this vehicle.

This past Saturday I disconnected the MAP sensor and drove about 60 miles - many starts and stops - and there was no change in in the issue.

I have not found a vacuum leak.

Can somebody guide me to a link showing all vacuum tubes on a 3800?

Could this be related to the throttle position sensor?

Why did you disconnect the MAP sensor for this issue? You sure you did not get a bad replacement MAF sensor?

The P0171 DTC indicates a short/long term fuel trim problem with can be caused by an intake system manifold vacuum leak, pre CAT converter 02 sensor or even a bad MAF (mass air flow) sensor depending on what the values are with a full function odb-ii scan tool which Autozone does not have or use.

Also, Autozone's national corporate policy is they are not supposed to reset any SES/CEL light and therefore no existing DTCs will be cleared. Plus only scan if the SES/CEL light is on.

In order for existing DTCs to clear on their own after the requisite drive cycle(s) the problem has to be resolved or fixed first.

Why did you disconnect the MAP sensor for this issue? You sure you did not get a bad replacement MAF sensor?

I was following the path of another thread with a similar issue. I am certain I did not get another bad MAF, the car was running utter crap and simply changing the MAF fixed it immediately.

At this time I feel the MAF and the high idle are unrelated in that the second issue - high idle - did not occur until a week or more after the MAF.

Yesterday I replaced the IAC and during my test drive it seemed to be running perfect correctly for me - much faster at returning to idle. Since it is my wifes car she is going to be the one to notice sooner than I will.

In order for existing DTCs to clear on their own after the requisite drive cycle(s) the problem has to be resolved or fixed first.

I do understand how they clear. I have one code that has been existant for about a year or more and it has to do with the selenoid in the trans - a known issue. I would like to clear the codes and see what pops up and how soon.

I do understand how they clear. I have one code that has been existant for about a year or more and it has to do with the selenoid in the trans - a known issue. I would like to clear the codes and see what pops up and how soon.

Best thing to do like many of us is invest in an odb-ii scanner. Not that expensive and since you like DIY work it would come in handy.

On the P1870 DTC it is a type "A" DTC but doesn't mean a specific solenoid is bad. It normally triggers the SES/CEL light. It indicates you are getting excessive torque converter clutch (TCC) slippage that is out of specs when the TCC should be engaged. Greater than 200 rpms of slippage for more than 5 seconds and then stored in the Trans Slip Counter. At least 3 counts must be stored for the DTC to set. Generally it a transmission component slipping.

When was the last tranny service - ATF and screen filter?

We bought the car used from my step mother with 55k miles on it. It now has 112k miles. I have been thinking about getting the tranny serviced - lube and filter change - this summer but have not done so yet.

I would love to get an educated opinion of doing so at this time.

I am not so much a DIY'r out of desire but out of necessity as I really do not have the money to run to a garage everytime the car has a hiccup, though, I did notice the scanners are reletively cheap these days and might be a nice addition to the tool box.

All Fixed.

IAC fixed the revving issue.

Turns out the MAF I bought was defective, once replaced the car is running great.

Thanks for all the help.