Let me first say that I have found this forum to be EXTREMELY helpful as I have already replaced the intake manifold gasket (not fun) and given her a complete tune-up (spark plugs not so easy to get to) just based on what I have read in the D-I-Y section. Recently bought a 2002LS, 4.3L V6 CSFI throttle with 174,000 miles. Was aware of the bank2, sensor1 O2 sensor circuit SES light when I bought her and I plan on further diagnosing this later, but as of yesterday, she idles fine at start up (after a few fluctuations), but after a drive around town she idles b/t 3000-3500rpms when engine is placed in park or neutral. When I start her back up after shutting her down for a few minutes, the idle is fine (around 900-1000rpms). Tomorrow I plan on checking for vac leaks and cleaning/checking the IAC valve since from what I have read on prev threads, may be the most logical issues. It's been a full week with no issues from when I completed the IMG and I am not picking up any other codes on my reader other than the 02 sensor(P0155). Does anybody else have any suggestions on some basic intial things to check?? I think the people walking in front of my Blazer in the parking lot at at Walmart today thought I was revv'n up to mow them down. ANy help would be great.

 

make sure your air cleaner is tight and you maf is clean.

 

Well....When you say air cleaner, do you mean air filter or are you referring to the whole assembly that secures to the top of the throttle body? I did change the air filter as well when I changed the spark plugs. I know that would be too easy of a fix. Tonight I took a $43 shot in the dark and replaced the MAP sensor....of course that did not fix it. Yea, I know, should have just put the volt meter on the old one before feeling lucky, but one potential possibility eliminated...hopfully. Now I'm wondering if the two sensors that are affixed to the top portion of the throttle body could have gotten messed up when I cleaned the throttle body with carb cleaner as I was replacing the intake manifold gasket. What do think the likelyhood of that being the problem is. Yea, I now know that I should have just taken the darn things out before cleaning. Well, you live and learn. Any other advice?? BTW, I checked and could not find any vac leaks.

 

Yes i ment the whole thing all the clamps the one on top of the throttle body and if you mass air flow meter is clean. My money is on a vacume leak some where, even a bad line at the hvac system can cause these systems not as bad as you are discribing. How did you check for leaks?

 

So far I checked all clamps...tight. I checked and probed all vac lines and gasket seal mating areas I could get to with an extra vac line connected to my ear....no luck. I found it hard to discern what I was hearing...mostly engine noise I think. I felt and probed collection points of vac lines, but wasn't real successful with seeing what I was doing or probing since the main area I wanted to check was under the distributor cap assembly. I replaced the MAP sensor and IAC valve...no luck. I LOOKED at the MAF sensor and it LOOKED clean. After replacing the IMG, it ran fine for about a week. I then changed the wires, plugs, distributor cap and rotor and air filter. I changed the plugs using the "removing the two front wheel method"....still not an easy chore, esp. that darn plug behind the steering shaft. The very next trip is when I developed the problem. Just like now...it started and idled fine at start-up..around 1000 RPMs. Initial shift to drive is correct, around 700RPMs. When I parked, it ran up to 2000RPMS. I tried to snap the throttle to get the RPMs down, and the RPM's jacked up to 3500RPMS. When I shift back to drive, the RPMs slow down back to around 1300-1500RPMS before the transmission engages to drive. I was cringing when I first attempted this, but luckily it didn't slam in at the 3500RPMs. If I turn her off and wait a bit for her to cool down, she usually idles back correctly and then the process starts back again. On a side note...I have since had to replace the radiator...multiple leaks (it was original radiator) and my flushing probably attributed to that. My leaking oil cooler to oil filter lines (to radiator) were also replaced. Atleast the girl isn't leakin coolant or oil anymore, but the probable vac leak is driving me nuts!!! Not to mention my front brake pads will need changed in very short order. I'm praying that I can get all this stuff fixed and I'll be set for a while, but in the mean time, I fear having to tear down the TB, air plenum to re-evaluate the sealing surfaces. My wallet is def taking a hit...but I AM DETERMINED and have developed quite a new vocabulary. HeehEe. I may take some carb cleaner and spray it around the areas where the gaskets meet to see if any of it gets sucked in before tearing stuff down again. Is this acceptable?? Any help would be great.

 

Start the truck up, if you can get it to idle for you use starting fluid or something like it. I use a propane torch without it lit and spray it every where under the hood. Little at a time when you get a idle change you know closer where to look.

I was reading a thread a lil bit ago where a guy had the same problem turned out he had a cracked up intake manifold.

 

Ouch....Let's hope that isn't the case. Yesterday, I changed the front brake pads and today I cleaned the MAF sensor. I haven't had a chance to spray around the seals yet. When I was bolting the Intake Manifold back on, because I couldn't get my hands on a low torque torque wrench, I bolted the bolts on all even at 24 quarter turns with my socket wrench...that's how many it took to get each one off. I wonder if they are not tight enough. I guess I'll find out soon. Oh... I also replaced the PVC valve as well. The truck runs better, but consistently idles at 1700RPM's after driving around and putting in park. What should it be idling at when in park and in drive? Right now it's 700-800RPMs in drive and 1700RPMs in park. Thanks for your suggestions. I'll keep you posted.

 

OK...update...Searched for vac leaks again with extra ear/vac hose probing..no luck. Tried spraying carb cleaner around the gasket seals of TB, IMG and air plenum with no leaks detected. Felt the tube leaving my PVC valve and felt some unusual vibration/sputtering through the tube. Took out new PVC valve (purolator Part#2057) and compared to old, but still good ACDelco PVC valve and noted that the pintle on the AC valve had a "E" stamped on it whereas the purolator valve had an "F". Also noted that on the purolator valve, there seemed to be considerable vacuum noted/heard thru it at idle and when I would cover the end with my thumb, the engine seemed to idle down to the smooth and correct RPM. So I thought.... ahhh haaa! I was given the wrong PVC valve! SO, I cleaned and put the ACDelco PVC valve back in and......no change except that it did fix the air vibrations felt thru the tube coming out of the valve. Also.....I AM GETTING A B2,S1 HO2S CODE....It had this code when I bought the truck and the previous owner stated that it had been like that for 2 years with no change to her MPG's or performance. I did not notice the symptoms I am having with high idle in park and neutral after driving around until AFTER I changed the plugs and wires to AUTOLITE (I know now that these are not recommended) and the air filter (purolator). The only other thing I have done is cut a wire tie that I had LOOSLEY wrapped around the throttle cable near the fire wall to help keep the left side plug wires from contacting the hot valve cover and exhaust manifold. Oh yea..I also took the TB off today and cleaned the heck out of it. I also took the IAC valve and TPS out and cleaned the IAC bore with a tooth brush too. Still....no change. I saw a previous thread from ABBY showing the EXACT symptoms my blazer is displaying titled HIGH IDLE (I think). Unfortunately, I have done everything that was suggested to her already and there was no update on a fix from her. What else......When I did my IMG, I am embarrassed to say that I had some kind of plastic spacer that fell out of the bottom and I did not put it back because I couldn't figure out where the heck it went and it looks pretty insignificant. Now I am wishing I had done more research on what this mystery part is. I'll try and include a pic of it. ALso today, I re-tightened all of the TB, air plenum and IM bolts. I don't know what else to do. I plan on diagnosing and/or replacing the affected O2 sensor mentioned above. I am hoping that maybe the "default" operation of this bad sensor/code is why the blazer is idling as it is and that maybe I just didn't "clue-in" to this idling problem until I had put everything back together from doing the IMG. Well, we'll see. Thanks for your input jacobcnc...I am surprised that no one else has had any suggestions. I'm definently ready to swallow my pride on this one. Anyone???

 

Are you sure your IAC valve is working properly?

What happens if you disconnect and plug all of the vacuum lines off of the intake?

 

I'll check and see about plugging all the vac lines next time I get a chance. Today, I correctly diagnosed/replaced the bad O2 sensor using the "switch" method read about here, and fixed the SES light, but no change in the other symptoms. I'm ready to pull my hair out! The IAC valve is brand new so it SHOULD be working properly. It's weird...Blazer does fine when first starting up and driving, but give it a couple of miles and at stop signs/lights, the truck idles in drive at 1000rpms and wants to drive itself in residential areas or any area 35MPH or below. I drive home, put it in park and it idles at 1700 everytime. If I rev it to 3000rpms it stays at 3000 and the only thing I can do is turn it off or put it in gear to drop them down. Thanks for your help, I'll keep you posted.