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Problem after cleaning throttle body.

65K views 17 replies 11 participants last post by  samlab1 
#1 ·
Hi all, new here. Found this place when looking to change the fuel filter.

Anyway, my mom said her 2002 TrailBlazer isn't running "the same" as it used to. I never drive it myself so I really didn't see much problem with it. But she insists it is more sluggish than usual.

So I planned to change the air filter, plugs and fuel filter. While searching for this I found many treads that people all had good luck simply cleaning the throttle body out. It has 101K on it at the moment and as far I I know the air filter was changed maybe 1 or 2 times, fuel filter and plugs were never changed.

Here is the article I used:
http://forums.trailvoy.com/articles.php?do=viewarticle&artid=91

Anyway, first I change the air filter to a K&N filter and at the same time I follow the instructions to clean the throttle body. It wasn't nearly as dirty as the one in the picture but I cleaned it and everything seemed to go as the instructions said it would.

So i put it all back together, triple check connections, and start it up. During the first 5 minutes all seemed OK. Was idling around 1100 RPM and throttle response (while in park) seemed instant. Well the problem is the longer I let the truck idle the RPM gradually kept getting lower and lower at idle. Eventually it seemed to settle at 600 RPM. I have no idea if that it good or not, but the problem is if I let it sit for about 30 seconds, apply throttle it seems to bog\hesitate then jump to 1200-1500 rpm, then I let of the throttle it drops to 700 RPM, then back to 800-900, then back down to 600. So letting off the throttle it jumps around a bit before settling back at 600 rpm. (Now if i rev it to 1500, then let it settle to 600 , then immediately rev again I hardly see the bog at all, but let it sit 30 seconds to a minute at it bogs on initial acceleration.)

I have not taken it for a drive in fear that something is wrong, so all this was done while in park and revving the engine to 1500 slowly.

I had driven the truck not too long ago and I am almost positive it idles around 1k and I don't remember this hesitation I am experiencing that is very obvious right now, almost as if it wants to stall, but the engine doesn't get to the point where it shakes or sputters.

Any advice? Or need more information?

Thanks
 
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#3 ·
I had that happen when I put my new system in and cleaned my engine a bit. I don't know what it is, but driving, it's fine for me. Take it for a test drive up and down the street and see what you think.

For me, it settles out as soon as it's put in drive, but even now, after a few months, it still does it SLIGHTLY when I rev in park.

but anyway, take it for a test drive and see what you think
 
#4 ·
Yes. 600 RPM is the target idle speed. A bit higher when cold. But since you disconnected the battery to clean the TB, you have to drive it for a while (30-60 minutes?) to get the PCM to relearn the adaptive tables it needs to predict where to put the throttle for various RPMs. You're teaching a baby to walk, and pulling the battery just erased all the lessons it's spent years learning.

If you don't have the Service Engine Soon light on, then there's nothing so horribly wrong that you can't take it for a drive.
 
#5 ·
Thanks for the reply, if that is the case then the RPM seem fine and I can assume the plugs or fuel filter are to blame. maybe the clean throttle body made the bog more obvious? I would believe that, but the fluctuating RMP after I lift the throttle is bothering me.

I did pull 1 plug out to inspect it, it seemed OK for 101K. I would have replaced them but AutoZone sold me Bosh plugs because they said AC Delco didn't make them for my truck. I read on here they infact do and the Bosh plugs suck. So I have to find a place that has AC Delcos.

I can take a picture of the plug if you think it will help. Just trying to figure out what I am chasing here.

BTW, nice site, wish there was one like this for pontiac.

Thanks
 
#6 ·
LOL, wow, this forum really moves! My last reply was after the first guy responded, then I see 2 more once I hit post!

OK, now I feel better about taking it for a test drive. Sounds like my truck is running like it should. I don't see the service engine soon light on so I'll try it out tomorrow (It is already dark for me, so I'd rather do it in the daylight in case I have a problem).

Thanks
 
#7 ·
Sounds normal. I Seafoamed mine today before changing the oil. Ran a little less than 1/2 can through the vacuum line and added the rest to the oil. Then I let it idle to clean whatever it would.

600-625 is the correct idle. Usually on starting, mine will go up to about 1100-1200 when cold, then start dropping. There is a lag in revving, primarily due to the drive by wire system. When I rev it, the RPM's go up (1100), down (700-800), up slightly (900 or so), then settles back down (700ish). Once the temp needle starts to move, it is usually on 600 at idle. I don't think you have anything to worry about, but it will drive a little funny while the PCM relearns.

At 101k, you probably should go ahead and do the plugs anyway. Can't hurt.
 
#8 ·
Thanks sctb, what you just described sounds like what is happening to me. Since it isn't my truck and my 07 GMC Sierra doesn't do it i assumed it was something wrong.

Just to be sure we are on the same page, i found this Youtube video of another member on here, he videos the RPM and also notes the second rev in RPM is not his doing, mine looks the same.

http://www.youtube.com/watch?v=xOVUq4PJmnw

I'll take it for a spin tomorrow and see how it is while in drive. My concern is when at a stop, but I'll report back tomorrow.

Thanks
 
#9 ·
:yes: That's it. Mine does same as the video. I'm pretty sure it has to do with the drive by wire. Even Seafoaming, which promises less hesitation, won't totally fix it...there will always be a slight lag when you press the throttle and when the engine responds. Then it bumps the RPM when it settles out. Why? Who knows except GM and the software. Possible, I guess that the butterfly in the throttle body is resetting itself?? Or some other slight adjustment the PCM is making??
 
#10 ·
I took the truck for a trip today, about 90 miles round trip, about 75% highway. So far everything seems fine, runs at 2100 rpm at 70 mph. I never experienced any bogging or hesitation through the entire trip. It does still do the weird throttle jump when in park just like that video, but everything else seems fine.
 
#11 ·
I was buying a new throttle body, for it's sensor of course, and there was an AC Delco rep who had just finished giving a training, and he told me the reason I was having to buy my throttle body was because when he asked if I had ever used a cleaner on the butterfly valve I said I had.

He told me Delco says that is never to be done as it will cause the sensors to fail over time. If anything, he said to simply wipe the area, but that as long as the air filter is changed regulary and Top Tier gas is used, there is never going to be a reason to clean the throttle body, or even the fuel injectors for that matter. Although he did say if for some reason bad gas is used and it needs cleaned, then ONLY Techron fuel system cleaner is to be used, otherwise the additives in the other fuel treatments will harm the parts.
 
#13 ·
Yep, it's the drive by wire technology. My '05 Chevy colorado and my '04 Envoy do the same thing. Doesn't do it as bad after I cleaned the throttle body though. Once you get some of that carbon off their it shouldn't stick as bad. As for you "rep" he doesn't know what he's talking about. Just make sure the carb/throttle body cleaner you are using is "sensor safe". It'll say it on the bottle. Good luck.
 
#18 ·
Heres what I did....I had replaced the vvt, cam sensor, belt, bearings and coils...then it starting going caput at start up especially when turning the air on...or starting getting worse in fact it went kaput entering traffic from house....frustrating.....but its working now....i even cleaned the throttle body off and on the car...nope nothing changed. Once the car was warmed and on the road just like normal....yesterday I put on a brand new Throttle body ACDelco 253-12095...from Amazon...says made in Germany ACDelco....pulled fuse 10 and 28 prior also buy the new gasket...this is so simple a baby could do it....8mm and 10mm wrench....1/4 or 3/8's your choice....installed....put fuses back in....no ac on....turn to run 3 times....after that turn car on...let idle for 5 minutes. Turn off for 1 minute....start car and drive normally a mile or two then turn on ac system....drive back....problem fixed. The key is that if your well above 100k in my case 226k this unit will take a dive....cleaning them works but the actual problem rests in the electronics in the throttle body taking a dive. Hope this helps. You'll notice how smooth the car drives immediately with a new one installed....only buy ACDelco on these cars.
 
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