P0108 and MAP troubles
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From: Baton Rouge, La. and sometimes Houston Tx
P0108 and MAP troubles I've been consistently setting the P0108 High MAP voltage code for a month or so now. I have a trouble shooting sheet from GM that I have went through and haven't solved the problem yet. The voltage at idle ranges from 4.17 or so to about 4.33 and 4.3 is the max at idle to prevent the code from setting. I replaced the sensor and verified that there are no vacuum leaks on the car. Sometime after accelerating and returning to idle it seems that the car idles higher for a few seconds or stubles and then returns to idle. As far as performance the car seems to be running fine. When the idle goes up it sets a P050x code for high idle. I'm not sure if the size of the cam is causing a low vacuum situation or if something else is wrong. It seems my powerbrakes and powersteering are iffy since the new cam but don't know if the lack of vacuum is causing the problem. Any suggestions are appreciated.
Thanks
Thanks
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From: College Station, Tx
Re: P0108 and MAP troubles P0108 is high MAP,not high MAF I believe - which you get from not enough vacuum at idle (as your surmised). What kind of vacuum readings are you getting - while you cam is large, for 422" and with a solid roller you should still be fine. What kPa values is your MAP sensor giving you? What RPM is your idle set to, and what kind of timing are you seeing there?
Thread Starter
TECH Enthusiast
Joined: Nov 2001
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From: Baton Rouge, La. and sometimes Houston Tx
Re: P0108 and MAP troubles The idle is bouncing from 800-900 and is set at around 850. It goes as high as 1100 once coming back from acceleration and returning to idle but settles back down. I see from 85-92 kpa at idle using the scan tool and the voltage is normally below 4.3V but tends to go over at least once every ignition cycle and set the p0108 code. The spark advance is showing anywhere from 9-14 degrees.
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From: College Station, Tx
Re: P0108 and MAP troubles The 85-92kpa value is your problem - that is a very low engine vacuum at idle - atmospheric is 100kpa - so you are pulling hardly any vacuum.
I would check again for vacuum leaks, anything unplugged, etc. - if there are absolutely none then you will need increase the idle rpm - that wouldn't be bad anyway as it would help get more oil to the heads at idle. You should experiment with the spark at idle and see if you can pick up any vacuum with increasing it.
I would check again for vacuum leaks, anything unplugged, etc. - if there are absolutely none then you will need increase the idle rpm - that wouldn't be bad anyway as it would help get more oil to the heads at idle. You should experiment with the spark at idle and see if you can pick up any vacuum with increasing it.
Re: P0108 and MAP troubles Dunno bout LS1 but LT1 idle voltage shoudl b aboue .5 volts and WOT is 4.5 volts.
Possible the cam was installed way advanced or retarded prolly also.
Possible the cam was installed way advanced or retarded prolly also.
Re: P0108 and MAP troubles Doh I thgouth i was reading about a TPS code 
High MAP makes sense a higher MAP is lower vacuum. Sounds liek the cam may be surging at idle a bit, goes into a timing table with low timing and vacuum drops.
The hihg idle thing may be a too big TB hole, or resolved when you get vacuum up a bit by timign tweaking or soemthing.
High MAP makes sense a higher MAP is lower vacuum. Sounds liek the cam may be surging at idle a bit, goes into a timing table with low timing and vacuum drops.
The hihg idle thing may be a too big TB hole, or resolved when you get vacuum up a bit by timign tweaking or soemthing.
