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Discussion Starter · #1 ·
Good Day all. Had to replace an injector on my son's 2000 300M. Replaced the injector and set the plenum back down, hooked every thing back up and once it started it would idle at no less than 2000 rpm's. The plenum gasket is new and the the seals on the rear egr tubes are new but when I put my hand over the throttle body, there was almost no suction. I have lifted the plenim and took ma peek to see if the gasket moved and it was still in place. Any body have any idea's.
 

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Discussion Starter · #3 ·
An update to this situation. There is now vacuum at the throttle body (might have somehow missed it the 1st time) and I sprayed some carb cleaner around the base of the plenum with no change in engine speed or tone. It has not displayed any codes. Got me and my buddies stumped.
 

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Discussion Starter · #8 ·
Check all vacuum hoses that connect to the upper intake manifold. Make sure no attaching nipples cracked / broken. Make sure all hoses intact and not cracked and oppositve end of vacuum hose is attached properly to its individual device. Leak at power brake booster hose can cause serious vacuum leak and raise slow idle speed.
Good thought. My son has a tendency to think brawn over brains and could have easily pulled or broke something.
 

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Discussion Starter · #9 ·
Good thought. My son has a tendency to think brawn over brains and could have easily pulled or broke something.
This morning I plugged all the vacuum ports started the engine with the same result. Pulled the IAC and checked the ohms and came up with 51.4 on the outer pins and 54.2 on the inners. Since I can't find the specs, is this thing junk or in the money?
 

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Discussion Starter · #13 ·
Thanks. That is good to know. So, not everything in this Haynes repair book is to be believed.
Checked the IAC as you suggested with zero reaction. Does anybody have an idea how I can check to see if the IAC is bad or ECM has gone south? The book I have is worthless as far as a procedure for this kind of check. Thank You in advance for any help the community can give me.
 

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Discussion Starter · #16 ·
The only way I have ever done an IAC/PCM diagnosis is with a capable scan tool. There are tests and commands that can be used to see if the PCM can control and the IAC can react.
If this fast idle just began after the intake manifold/fuel rail/injector service, I'm pretty sure you are dealing with a vacuum leak.
I would pull things back apart for a look.
I've had the plenum off twice to see if anything moved and came up with nothing. And, tried spraying carb cleaner around the base of the plenum and got no change. Still bugs me that the IAC didn't react as suggested. Just a thought, can I plug that IAC into my 99 LHS and try the same test without harming that ECM? Around here, scan tools are as hard to find as virgins after prom night.
 

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Discussion Starter · #19 ·
Tried the test and found out the IAC is dead. We'll get a new one and see where it goes from there. Unfortunately, it gonna take 3 days to get one. One of the few bad things about living in the middle of nowhere. Updates as they happen.
 

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Discussion Starter · #20 ·
Tried the test and found out the IAC is dead. We'll get a new one and see where it goes from there. Unfortunately, it gonna take 3 days to get one. One of the few bad things about living in the middle of nowhere. Updates as they happen.
HELP! Just installed a new IAC and checked to see if would move before I cranked it and nothing happened. Am I looking at a bad ECM?
 

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Discussion Starter · #21 ·
HELP! Just installed a new IAC and checked to see if would move before I cranked it and nothing happened. Am I looking at a bad ECM?
Took it for drive and it worked itself out. Thanks for everybodies help. Now, does anybody have a clue where to find a throttle cable for a 300M? The cable on this one is frayed and probably won't last much longer
 
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