Idle Issues
01-05-2006, 12:48 AM
#1
Racer
Thread Starter
Idle Issues
My 87 951 is having idle issues. When it's cold, sitting for a few hours in 30 F temps, at start up it runs terribly. I have to keep the revs up to 1500-2000 to keep it running. It's also putting out alot of smoke, although being cold outside makes it difficult to quantify how much more than usual. After a few minutes of warming up it will idle and run fine. But then the reverse happens. At zero throttle, it idles at 2100, sometimes dipping to 1300 then back down to a normal idle. The mods on it are all minor. Ideas?? Thanks
01-05-2006, 02:06 PM
#2
Racer
Join Date: Aug 2003
Location: Fairfax Va
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I have the same problem sometimes, i think i narrowed it down to a vaccum leak. It still does get a little bit rough but its not down in the 700-800 rpm ranges. Possibility could be that the oil is still very thick since it hasnt been warmed up to temperature, dunno what it really is though. Crank Scrapers may help out
01-05-2006, 11:37 PM
#5
Addict
Rennlist Member
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kwdrus: You can bypass the ISV by pulling the vaccum connection off of the intake manifold (the ~1/2" line, the one closest to the firewall) and then plugging the port on the intake. You can also electronically disable the ISV by bridging between plugs B & C on the test port.
The ISV is only supposed to operate when the engine is cold and when the A/C is on. If you bypass it and your idle smooths out and the elevated idle disapears then that's likely the problem. Bsed on your symptoms my guess is that it's the ISV. You can attempt to clean it by dousing it with carb cleaner or you can buy a rebuilt one from 944online.com for ~$80 or a new one for $140. Either way you get to remove the intake manifold
As you can tell I'm chasing an idle problem as well, although mine is only when the engine is warm. I'm suspecting the DME temp sensor is the issue, the DME seems to think the engine is still cold, even after it's warm, which means it's using the wrong idle maps. The O2 sensor then tells the DME that the mixture is wrong, but the DME can't compensate sufficiently b/c it's limited by the cold temp idle map, resulting in uneven, surging idle.
Or that's the theory anyway, we'll see when I get the DME Temp sensor installed!
HTH,
Greg
The ISV is only supposed to operate when the engine is cold and when the A/C is on. If you bypass it and your idle smooths out and the elevated idle disapears then that's likely the problem. Bsed on your symptoms my guess is that it's the ISV. You can attempt to clean it by dousing it with carb cleaner or you can buy a rebuilt one from 944online.com for ~$80 or a new one for $140. Either way you get to remove the intake manifold
As you can tell I'm chasing an idle problem as well, although mine is only when the engine is warm. I'm suspecting the DME temp sensor is the issue, the DME seems to think the engine is still cold, even after it's warm, which means it's using the wrong idle maps. The O2 sensor then tells the DME that the mixture is wrong, but the DME can't compensate sufficiently b/c it's limited by the cold temp idle map, resulting in uneven, surging idle.
Or that's the theory anyway, we'll see when I get the DME Temp sensor installed!
HTH,
Greg