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Pulsating Idle when engine is hot, almost stalls

 
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jstrm



Joined: 28 Jun 2011
Posts: 2
Location: Englewood, FL

PostPosted: Tue Jun 28, 2011 4:34 pm    Post subject: Pulsating Idle when engine is hot, almost stalls Reply with quote

Tech help for this very weird problem. BMW 328IC 1997. Once engine is hot it will start a gulping sound from under the intake manifold and the idle goes to pot. Its like gulp, gulp, gulp, then exhale at 1 second intervals. On the highway it gets the same effect like the engine is cutting out on every gulp. Any help would be appreciated.
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PJK



Joined: 14 Feb 2002
Posts: 1829
Location: Shingle Springs, CA

PostPosted: Thu Jun 30, 2011 1:04 pm    Post subject: Re: Pulsating Idle when engine is hot, almost stalls Reply with quote

I'm sure your intake manifold is slightly different from that on my "93 but I'm guessing it it similar.

Under the manifold there is the idle control control valve. At the inlet to the valve is a hose which connects to a tap on the large curved hose from the air flow meter to the throttle body. At the outlet the the valve is a hose which connects to a plastic fitting which plugs into the intake manifold. Check all of those components for leaks. If you can't find any leaks clean out the ICV with carburator cleaner and check the fault codes.

Phil


jstrm wrote:
Tech help for this very weird problem. BMW 328IC 1997. Once engine is hot it will start a gulping sound from under the intake manifold and the idle goes to pot. Its like gulp, gulp, gulp, then exhale at 1 second intervals. On the highway it gets the same effect like the engine is cutting out on every gulp. Any help would be appreciated.
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jstrm



Joined: 28 Jun 2011
Posts: 2
Location: Englewood, FL

PostPosted: Thu Jun 30, 2011 4:32 pm    Post subject: Reply with quote

Thanks for the tip. Its a jungle under there of pipes and hoses. From what I can see there is a circular diaphragm thing that is making the sucking sound. I'll have to wait for the weekend to dig in and check for leaks. I'll try the carb cleaner trick.
I do still have a question, what actually controls the ICV? The way it is pulsing in a rhythmic manner, it seems to be controlled externally and sucking air and then recovers on its own for a few seconds, then starts the cycle over again.
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PJK



Joined: 14 Feb 2002
Posts: 1829
Location: Shingle Springs, CA

PostPosted: Fri Jul 01, 2011 12:40 pm    Post subject: Reply with quote

The ICV is a cylindrical solenoid air valve. It is controlled by the engine management computer (DME).

I would check for air leaks before trying to clean the valve. The fact that you are hearing air leaking from under the manifold points in that direction. With the "false air" (air not accounted for by the air flow meter) getting into the intake manifold the DME can't control the idle and the fedback control loop can go unstable.

This job is going to be a royal PITA. If you rempve the air box you may be able to get in there. Worst case is you may have to remove the intake manifold to gain access. If you have to remove the manifold consider changing all the coolant hoses while you are in there. I just did mine before my unfortunate event (intake manifold and all). There were decomposed hose fragments in the heater control valve. Got my heater working fine just in time for summer.

I noticed a tool at Harbor Freight which may help you see under the manifold. It is a little camera on the end of a flexable tube and an LCD screen. It is about $150. I have seen similar tools by Milwalkee at Home Depot for about $450. At $150 I am very tempted.

Phil


jstrm wrote:
Thanks for the tip. Its a jungle under there of pipes and hoses. From what I can see there is a circular diaphragm thing that is making the sucking sound. I'll have to wait for the weekend to dig in and check for leaks. I'll try the carb cleaner trick.
I do still have a question, what actually controls the ICV? The way it is pulsing in a rhythmic manner, it seems to be controlled externally and sucking air and then recovers on its own for a few seconds, then starts the cycle over again.
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