Years ago my 1985 S-10 pickup also had an very *unstable* idle. At that point I didn't know about READING the engine trouble CODE - so on a hunch I changed the throttle-body fuel injector. This gave the truck more power, but the idle was still terrible and kept changing a whole lot & died at stop signs, etc. Finally I found how to read that trouble code = On Board Diagnostic = "OBD". I only had to connect a short piece of wire between two terminals on the socket where the diagnotic computer plugs in & the Check Engine light gave a flashing code readout, over and over. That code showed that the MAP sensor (manifold air pressure) was BAD. Replaced the MAP module (which was easy) and the truck idled real good. The book telling that was found at a Pep Boys store & cost about $13.
- posted
16 years ago
Well, after 333,000 good miles my 1987 E16S Sentra has developed a
> very unstable idle. It started out as occasional stalling during warm-
> up. It got worse and began a rolling idle (rpm up and down) when cold
> and during warm up with more frequent stalling during warm up. Now
> there is always a rolling idle whether cold, warming up or hot. Once
> warmed up it will sometimes idle at very high rpm and sometimes it
> will not idle at all but flat out stall as soon as the clutch pedal is
> depressed. The carb primary and secondary are fine as once you get
> past idle it runs great. Also, it is an idle speed problem and not an
> idle mixture problem as there is no black smoke and the plugs look > fine. >
> There is an idle speed control actuator which operates on vacuum
> providee by a vacuum control modulator (VCM). Due to the rolling idle
> I suspected the VCM, so I tested it per the factory service manual and
> it checks out OK. The voltage (12v) and the vacuum (2" Hg to 3" Hg)
> are within specs. There are two small air filters that filter outside
> air to the VCM and the idle speed control actuator and they are not
> clogged. So I'm now thinking that the idle speed control actuator
> itself is going bad.
>
> Has anybody had any experience repairing/replacing this part? Can it
> be replaced without removing the carb from the manifold? Anybody know
> of where one might be able to buy one short of a junk yard (likely to
> be in worse shape than mine). I'll appreciate any advice. Thanks in > advance. Al >