High idle and Cruise 'idle'...

Hi guys...this is a post copied from my post over at pontiacbonnevilleclub.com. I know you guys are very knowledgeable and I know someone will come up with something!

I have a '00 SSEi with a 180 degree thermostat and AL605 spark plugs, and Intense FWI. No other mods. The problem started this morning when I started the car. Idled normal for about 10 seconds then idle jumped from 1000 to ~1500. Weird. So I let it sit for 30 seconds or so and it came down to 1200. I got on the road because I had to get to work, and the car coasted at high enough an RPM that the car was actually accelerating itself on flat surfaces (35 mph, 3rd gear, 1700 RPM). No engine light.

So I stopped about 2 miles from my house seeing this was a problem, popped the hood and heard no obvious leaks or anything visually awry. I shut off the car, started it back up, everything operated perfectly.

After work (10 hour shift), car did the same thing...idle started fine and popped up to 1500. I shut off the car and started it again and it was fine all the way home.

I did have my scanner with me the entire time but didn't think to plug it in. I know you guys probably need more information (from the scanner) and will be glad to provide what I can, though my scanner is limited in what I can view.

Thanks for your help everyone!

-Andrew Z

EDIT: Just scanned the car real quick. The idle didn't jump at all. The IAT was 110, and my LTFT was 16.4. No good. My first instinct is vacuum leak, but there's a storm brewing outside. - I'll have to play with it tomorrow. Any new thoughts now?

Z-type wrote:

Hi guys...this is a post copied from my post over at pontiacbonnevilleclub.com. I know you guys are very knowledgeable and I know someone will come up with something!

I have a '00 SSEi with a 180 degree thermostat and AL605 spark plugs, and Intense FWI. No other mods. The problem started this morning when I started the car. Idled normal for about 10 seconds then idle jumped from 1000 to ~1500. Weird. So I let it sit for 30 seconds or so and it came down to 1200. I got on the road because I had to get to work, and the car coasted at high enough an RPM that the car was actually accelerating itself on flat surfaces (35 mph, 3rd gear, 1700 RPM). No engine light.

So I stopped about 2 miles from my house seeing this was a problem, popped the hood and heard no obvious leaks or anything visually awry. I shut off the car, started it back up, everything operated perfectly.

After work (10 hour shift), car did the same thing...idle started fine and popped up to 1500. I shut off the car and started it again and it was fine all the way home.

I did have my scanner with me the entire time but didn't think to plug it in. I know you guys probably need more information (from the scanner) and will be glad to provide what I can, though my scanner is limited in what I can view.

Thanks for your help everyone!

-Andrew Z

EDIT: Just scanned the car real quick. The idle didn't jump at all. The IAT was 110, and my LTFT was 16.4. No good. My first instinct is vacuum leak, but there's a storm brewing outside. - I'll have to play with it tomorrow. Any new thoughts now?

This car have any work on it recently? what work? Please comment.

Is your TPS reading correctly?
Maybe try cleaning the MAF and IAC.
And of course check for vac leaks (is your vac fluctuating at idle more than like 0.2?)

Yes...I've had the supercharger off twice to fix the bypass valve and the intake gaskets. That is all the major engine work, and that was back in March. I replaced the T fitting under the snout when I did the intake gaskets because it was brittle. I also replaced the vacuum line that goes from the EVAP solenoid to the throttle body because the rubber parts of the line we dry. All other lines visually look fine. I'm going to do another vacuum leak test tomorrow afternoon.

I don't know that my scanner can read my TPS. If it cant, what terminals do I test with my multimeter and what numbers should I be looking for? I actually just cleaned the MAF a few weeks ago and the values seem correct on the scanner. I can't read the IAC, but I cleaned it when I bought the car in February. On the boost gauge on the dash, it is fluctuating between -7.5 and -6 at idle in Park - far too low, I know. It shows a stable -12 on the scanner though .

Only other things I've done are replaced the EVAP vent valve underneath the car because of an EVAP leak, and that has been fixed for 3 weeks. This came out of seemingly nowhere.

I was going to call faulty IAT sensor until you said it read 110. But you also said the idle was fine that time. Next time the idle jumps up, try to log a scan of the basic parameters. Check IAT value when the RPM surge occurs. If it drops to -38, you have a break in the IAT sensor wiring, connector or sensor, causing the car to high idle at random times.

I have to pick up a Grand Prix to detail in the morning, but when I get home (which will be early, and I should be sleeping) I'll give the car a start since it'll be nice and cold and write down some figures. I haven't figured out how to log on my scanner yet. Thanks guys!

OK Andrew I read here that you had hte blower (supercharger) off twice. I do not reas that you cleaned the downwind side of the throttle body.

If you have not removed and cleaned the throttle body I suggest you get a TB base gasket then pull and clean the thing with CRC's throttle body cleaner. You will be dismayed at how much tar has accumulated there. Also when you do that remove the MAF and IAC (Idle Air Control) before you clean the TB, and clean the IAC with the TB cleaner (or consider just replacing it they are less than $40 -- even the Duralast from Autozone is made in the US and decent quality although not exactly OE, if you put 'em side by side you can see the differences). ALso clean out the SC inlet and the EGR inlet ports while you are in there.

Albertj

Thanks Albert...No, I forgot to mention that I did do a Seafoam top end cleaning too, about a month ago. I didn't do the throttle body by itself though. I will try to get to that today but I'm going to look for a vacuum leak too.

I got to scan the car this morning when I started it and....nothing happened. All systems normal, no higher idle, nothing. I did notice, however, that I misinformed you all...my LTFT is +16.4 not NEGATIVE 16.4 at idle. So I think I'm confused which way the car is running. Positive means it's running lean and adding fuel? That would only confirm a possible leak. While driving, the LTFT seemed to act normal, except when coasting it would be +16.4 like at idle.

I'm going to do this car detailing then work on the Bonneville. I'll let you know if I find anything this afternoon. Thanks!

We knew you meant positive (lean). 16.4 is the max value for + LTFT. There is another thread dealing with a similar issue here: https://rivperformance.editboard.com/t8434-ltft-164-for-idle#131698

Might be helpful to you once Mr.Riviera solves his issue.

You know, I kinda wonder if the IAC has simply failed or is now sticking?!?! thoughts?

Could be sticky...or it could fail. Failure is always an option lol. I wish I could read what it was reading on the scanner though.

I did a vacuum leak test with the throttle body cleaner (which I just happened to have and brand new can of CRC for a rainy day) and i found nothing whatsoever. On the top of the blower where the boost actuator and brake vacuum line attach theres a cap on the one vacuum nipple, it was slightly cracked, but not leaking yet. I replaced it. I watched my scanner the entire time I was leak testing and the 16.4 didn't budge.

Z-type wrote:

Could be sticky...or it could fail. Failure is always an option lol. I wish I could read what it was reading on the scanner though.

I did a vacuum leak test with the throttle body cleaner (which I just happened to have and brand new can of CRC for a rainy day) and i found nothing whatsoever. On the top of the blower where the boost actuator and brake vacuum line attach theres a cap on the one vacuum nipple, it was slightly cracked, but not leaking yet. I replaced it. I watched my scanner the entire time I was leak testing and the 16.4 didn't budge.

You can't really just clean the IAC - that is, you **can** remove it and clean it with throttle boday cleaner. You will use a lot of TB cleaner to get it clean. You have to get it pristine including the pintle, behind pintle, the shaft, spring and spring seat.

Problem then is the place it mounts will be mad dirty, you have to clean it and because it is a chamber with a 90-deg bend the only way to do that right is remove the TB. (get that gasket first) With the TB off, you then clean things up. Would not hurt to get a pie plate or (throwaway food container and soak the TB bottom in cleaner for a while, then go after it with a chop rag and spray cleaner. Again, if you've not cleaned yours before, it will be a tarry mess. And clean the SC inlet... be sure not to spray cleaner into the inlet such that it goes into the SC oil, consider sticking a rag already damp with TB cleaner into the opening then spray to clean the IAC and EGR passages.

If you have the neoprene impregnated gasket paper you can use the old gasket to sketch and cut yourself a new one with a stencil (x-acto) knife. Thing of it is if you were paying yourself by the hour at shop rates it will cost you lots more to make than to buy unless the auto parts store is far away. It's funny - I was at my Buick dealer for other stuff and asked about the TB gasket, the parts manager just chuckled. They don't stock them themselves, they get them from the local NAPA or CarQuest depending on which is next to run an order to their shop.

Oh yeah while it's on my mind the TB is "water-cooled" so when you do this you can either drain some coolant (put it back in and burp the system when you are done) before you pull it or put a big shop rag under the TB to catch spillage and have some coolant on hand to burp and refill when you are done.

Ah i got cha on the IAC. Didn't think of the passage being filthy.

I don't think I'm going to get to the TB today. I'll at least pick up the gasket tomorrow after work so I know I have it. Thanks for all the info Al...I'll ponder over it until I get to cleaning.

The other weird thing about cleaning the IAC is the idle *will* run high (in my case dead-on 1000 RPM) until the PCM re-leans. You can force that re-learn using the Tech II or by driving the car for a while dead on 40 MPH using cruise control. I live in a rural area and there's a long stretch of road jsut perfect for that with limit of, ha ha, 40 MPH. Couple miles cruise down and back & the car was *very* happy (and my idle was not hunting anymore)

Also when you get that IAC and its passage in the TB pristine clean some instructions say you then have to push the pintle all the way into the solenoid body firmly, use your palm so you don't scratch it, before reinstall. Some other instructions say don't do that, you'll damage the IAC. In the factory manual (p. 6-923) for my '98 Riv the book says to press the pintle in manually until it sticks out less than 28 mm (1-1/8").

The manual says the PCM resets the IAC when you cycle the ignition on-off (NOT start the car). It says turn ignition on, then off; then turn ignition off. (go figure... and how does one do that on - off - off thing?!?) Then start the car & let it reach operating temp (195-deg).

Well... I am thinking the tech writer who wrote that does not work on cars.

But I kinda did it anyway. Turned ignition on, then off, then on , then off, then removed key. Then started car. And waited. When I did that and the car reached op temp the idle was stuck so to speak at 1000 RPM.

Now -- in the package insert with the new IAC there was a note saying the idle would be stuck at 2000 RPM until finishing a 40 MPH relearn cruise.

At this point I just shrugged my shoulders. Happy I was not at 2000 RPM but stuck with fast idle.

So I put it in gear, pulled out of the driveway and went for a 40-MPH cruise.

Anyway - in my experience during the relearn cruise the PCM really resets the IAC solenoid. It might fishbite a little teeny bit early in the cruise (mine did the first 1/2 mile) but it smooths out in I'd guess a mile or so.

Got back home, idle was down where it usually is (700-something) and I am smiling (a little).

For the $40 (or a little less) you might want to buy a new IAC... I did...

Albertj

I appreciate all the information Albert...you and most of the other guys always seem to have the best information and suggestions!

I apologize for no updates lately. Just the usual...annoyingly busy. Anyway, the Bonneville has been acting PERFECT ever since the day I made this post. The idle has been normal on startup and when warm, as well as cruising. I haven't scanned the car the past few days to check the fuel trims, but I can't imagine they'd be any different. The car has a ton of power, feels the same as my dad's Regal GS. So I got nothing for now. I still don't know when I'm going to get to clean the throttle body, but I know I need to now, since I haven't done it right yet.

Thanks guys...I'll update you when something happens.

-Andrew Z

Z-type wrote:

I appreciate all the information Albert...you and most of the other guys always seem to have the best information and suggestions!

I apologize for no updates lately. Just the usual...annoyingly busy. Anyway, the Bonneville has been acting PERFECT ever since the day I made this post. The idle has been normal on startup and when warm, as well as cruising. I haven't scanned the car the past few days to check the fuel trims, but I can't imagine they'd be any different. The car has a ton of power, feels the same as my dad's Regal GS. So I got nothing for now. I still don't know when I'm going to get to clean the throttle body, but I know I need to now, since I haven't done it right yet.

Thanks guys...I'll update you when something happens.

-Andrew Z

you can make a guess at how soon to prioritize cleaning the TB by how much the idle speed flutters at idle.

If the TB is pretty clean the tach will be rock-steady at idle.
If not, it will vary over time as much as +/- 50 to 100 RPM in the course of a minute.

What to do, next time you drive it, when you park and are ready to shut it down just put the car in park and let it idle ~ 30 seconds while watching the tach. That simple. The more perceptible the variation the sooner you should pull and clean the TB and SC/manifold inlet.

Albertj

Thanks Albert...I never knew that either. The idle always seems pretty steady but I never imed it or paid THAT much attention to it. I will do that next time I drive it. (it's been nice so the T-type has been out to play lately)

Thanks again!

Well, new update. The Bonneville has had the idling problem twice since I last chatted with you all about it. Today, on the way to the girlfriend's house, the idle jumped back up to 1500 again, so I stopped the car and popped the hood. I unplugged the IAC and nothing changed. I think it's probably a safe assumption my IAC is dirty or shot. I tried removing it but I broke the head of one of the screws off. Dammit. Luckily it's still secure and doesn't appear to be leaking vacuum right now. So I guess I need to replace the IAC.

So now I guess I need to find a bolt remover that's small enough. Hopefully the other bolt doesn't break.

Ok I replaced the IAC. Nice shiny new BWM or BDW or whatever that brand is. I can't remember for some reason. Anyway, I cycled the ignition on and off twice and did a re-learn - everything SEEMS ok. and normal, if not a smoother idle (if that makes any sense).

For some unknown reason, no local stores have throttle body gaskets, and they don't carry them (wtf?) so I'll be waiting for one in the mail before i clean the TB completely. I did do a decent cleaning of the IAC chamber which actually wasn't all that horrible.

The throttle body gasket is probably part of an upper intake manifold set, and not readily available separately. The upper intake set is probably more available.

At parts stores, yeah probably. I'll check on that. Wouldn't hurt to have an extra S/C gasket laying around for when I do my dad's intake gaskets, if that's part of the set.

deekster_caddy wrote:

The throttle body gasket is probably part of an upper intake manifold set, and not readily available separately. The upper intake set is probably more available.

I am surprised about that TB gasket thing. I confess that I got one from AutoZone...

Albert you just reminded me a new Autozone opened up in one of the towns near me! I totally forgot. I shall try that.

The place where you get it shouldn't matter as long as the brand is right, right?

Z-type wrote:

Albert you just reminded me a new Autozone opened up in one of the towns near me! I totally forgot. I shall try that.

The place where you get it shouldn't matter as long as the brand is right, right?

Place matters but point is check it our for yourself. My local autozone has improved since they hired this ex-Marine warrant officer as the commercial manager. He's not a tyrant but he does manage to set and enforce realistic expectations. They sold me a Fel-Pro TB gasket, more $ than Rock Auto but less headache than cutting it myself out of neoprene-impregnated gasket stock, which by the way will work fine. On teh felpro gasket I'd install it as is. On a cut-it-myself gasket I would smear a thin layer of brown form-a-gasket on it just prior to assembly or maybe use gasket shellac but the surfaces are machined so that I doubt it's really needed.

Albertj

albertj wrote:

deekster_caddy wrote:

The throttle body gasket is probably part of an upper intake manifold set, and not readily available separately. The upper intake set is probably more available.

I am surprised about that TB gasket thing. I confess that I got one from AutoZone...

Only because the TB gasket by itself is probably not as popular as a complete upper set. It depends on the size of the store, as to how deep their inventory goes.