I have a 1999 Pontiac Montana, It started having idle problems and hesitation in park and drive.

Tiny
MSHEPP37
  • MEMBER
  • 1999 PONTIAC MONTANA
  • 14,500 MILES
I have a 1999 Pontiac Montana, It started having idle problems and hesitation in park and drive. I replace the lower intake about 6 month ago along with the upper intake and tons of O-rings. Now this started I have already tried new plugs, wire set, fuel pressure regulator, map sensor, installed all new O-rings on the fuel injection rail and injectors, cleaned the MAF, new air filter. I checked for fuel pressure and spark coming from coils. Everything is firing. It starts easy. I figured a vacuum leak so I sprayed everything down while vehicle is running. I found one little spot that it made it changed idle but nothing really noticeable. I will address this too with new upper intake gasket. I have unplugged the EGR and throttle position sensor no change in idle at all. Pulled the MAF and vehicle will cut off so thats working. I have no check engine light on and has never come on since we have owned it. It has 145,000 miles. Could it be a faulty PCM or a burnt valve? This is about all I can come up with except maybe cam sensor and crank shaft sensor also.
Tuesday, May 15th, 2012 AT 2:04 AM

8 Replies

Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
The Idle Air Control Valve is the best place to go from here. It is located on the intake manifold near the throttle body.
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Tuesday, May 15th, 2012 AT 2:11 AM
Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
If you are looking for a source to guide you to reputable parts dealers, go to www. Carrepairlinks. Com
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Tuesday, May 15th, 2012 AT 2:12 AM
Tiny
MSHEPP37
  • MEMBER
  • 4 POSTS
Have unplugged the IAC sensor as well and it seem not to idle up or down. Or take the hesitation and shake out. I will try a new one and see.
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Tuesday, May 15th, 2012 AT 11:28 AM
Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
When you replace also clean out the prots with brake or carb cleaner. I prefer brake cleaner because it is easier on rubber and other platics. Also, make sure to spray from the outside in towards the intake manifold so you don't push deposits further towards the IACV and further clog the ports.
You Should also run a can or 2 of BG44K. You will have to go to a car dealership to get it and it is around $20 a can, but nothing else comes close to working like it does. It cleans deposits out of the entire fuel system and even removes carbon from the tops of pistons. All of the deposits end up in the oil so after running the 2 cans, use a full tank of gas without any BG and you might expect some things to act a little funny as deposits are removed. The oil will need to be changed if the engine is really dirty since the deposits will all collect there.
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Tuesday, May 15th, 2012 AT 6:12 PM
Tiny
MSHEPP37
  • MEMBER
  • 4 POSTS
Just curious, can you also do it through the brake booster and pcv valve vacuum lines as you can seafoam?
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Tuesday, May 15th, 2012 AT 7:07 PM
Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
I do not reccomend that as it is a, "quick way" that some say works as well. It also creates a tremendous amount of smoke and I am not comfortable with the possibilites for top end damamge or wear.
To truly be safe with this stuff, and I know SEA FOAM is good but BG44K is better, you have to have a full tank of gas to use a can. That should tell you something about how strong the stuff is.
I do not reccomend doing that at all. Use the cleaner as reccomended and it will give a deeper cleaning, remove more deposits and get to more places than the, "quick flush" will do.
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Tuesday, May 15th, 2012 AT 8:19 PM
Tiny
MSHEPP37
  • MEMBER
  • 4 POSTS
I have used sea-foam as indicated on about every vehicle I have and have never had a problem with it hurting or damaging the top end. As for the sea-foam it states to use it in oil, fuel and vacuum, about a 1/3 of can in each. Going in through the vac line gets to where it would not get just by running it through the fuel also. Anyway I have the upper intake off and it's in soak right now to get all that junk out. Would it be wise to go ahead, since I can get to the cam sensor to replace it while I have the chance or to at least ohm it out. I checked the torque on the lower intake and all seems fine there to. No leaks indicated either! Just trying to cover all my bases before I put this back together.
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Wednesday, May 16th, 2012 AT 3:27 PM
Tiny
DRCRANKNWRENCH
  • MECHANIC
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That sounds like a good plan.
All you can do is see how it runs. I would let it run 10 minutes before I made any judgements.
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Thursday, May 24th, 2012 AT 12:09 PM

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