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Dave Nova
Dave Nova, Pontiac Technician
Category: Pontiac
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Experience:  ASE Master Certification. GM World Class Certification
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2001 montana: intake manifold..van immediately idles..going down

Customer Question

I replace the intake manifold gaskets on 2001 montana. Once reconnected the van immediately idles at 300 rpm and then begins revving up to 4000 rpm an the back down. When going down it progressively ends at a higher poit i.e. 1200 then 1400rpm. No apparent vacuum hissing. I also rechecked the connections to the pvc and mass air flow sensor.
Submitted: 3 years ago.
Category: Pontiac
Expert:  Dave Nova replied 3 years ago.
Hello and thank you for using JustAnswer. My name is David and I will do my best to help you with your Pontiac problem.

Is the check engine light on when the engine is running?
Customer: replied 3 years ago.

No. And the engine continues to rev to 4000rpms but now only goes down to 2700 rpms and progresses to wear it only comes down to 3100 rpms.

Expert:  Dave Nova replied 3 years ago.
Unplug the throttle position sensor (3 wire plug at the throttle body) and see if the engine diles differently.
Customer: replied 3 years ago.
No difference. By the way when you press the accelerator the throttle cable will pull and the throttle opens but the engine does not rev at all it only revs during its "cycle"
Expert:  Dave Nova replied 3 years ago.
Check to make sure throttle blade is closing all the way. Sounds like there is a major air leak. Make sure vacuum hose to brake booster is installed at both ends. If it is then use carburetor (or brake) cleaner spray around the intake area with engine running. If idle changes with the spray, you have found your leak.
Customer: replied 3 years ago.
I inspected the vacuum line to brake booster and it is secure. I used brake cleaner to spray all areas of the intake I could access the rear side where the lower intak and the head meet is inexcessible while engine is running. There was no difference. Is there anything else you can thnk of?
Expert:  Dave Nova replied 3 years ago.
Yes, with the engine running, remove the oil filler cap from the valve cover and see if there is a large vacuum at the oil fill hole. Place hand over hole to check. If there is suction there then the vacuum leak is internal. This would indicate that one of the lower gaskets slipped out of place during intake manifold installation.
Customer: replied 3 years ago.

No vacuum leak at the oil fill hole. I also disconnected baterry and checked the prongs on the IAC TPS and MAF sensor plugs. I thought unplugging the battery might allow car to reset to starting idle closer to 1000 rpms and then climb but it is again over 3000rpms at all times. It is strange that yesterday it started at 1000rpms and climbed each timed it revved but now it just stay above 3000 and revs to 4000.

Expert:  Dave Nova replied 3 years ago.
Is throttle blade fully closing?
Customer: replied 3 years ago.
Yes. and it opens when the throttle is engaged even though the car does not respond by revving at all.
Expert:  Dave Nova replied 3 years ago.
If there are no external or internal vacuum leaks then the problem just about has to be in the idle air control (IAC) valve at the throttle body. Remove the valve and see if there is any carbon in the bore or anything that would keep it open. Clean the valve and bore with more spray and try running the engine again.

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Dave Nova
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