GrimGreg Posted February 12, 2013 Share Posted February 12, 2013 My 93 wants to idle at about 300-500 rpm, it idles smooth at that speed, but it won't keep the alt charging enough to idle very long. I haven't done much searching yet, but my best 2 guesses are either an IACV or TPS issue. Any other suggestions on what to look at for a cause? For the moment I just put a spacer in the stop bar on the throttle so it stays open more and keeps the idle up around 1200. Link to comment Share on other sites More sharing options...
Precise1 Posted February 12, 2013 Share Posted February 12, 2013 I've not had this problem, but the opposite where it will occasionally idle higher than normal (1000-1100) and not drop down to 850 RPM unless I wiggle the wiring connector clipped onto the TPS so you might want to try that. The wife's Matrix's idle used to hunt and surge a bit when cold. I sprayed down the throttle plate and IACV with throttle body cleaner and let it sit for a bit. Once I got it started and cleared, it idled smoother at a slightly lower RPM, and no more surging when cold. I could see both of these things being the culprit. First make sure that the vacuum lines aren't compromised and that the timing is right. B Link to comment Share on other sites More sharing options...
GrimGreg Posted February 13, 2013 Author Share Posted February 13, 2013 Yeah, first thing I checked was the vacuum lines, and I would assume that the timing is good since it ran smooth at 300 RPM. Going to clean up the intake and check my sensors when I get the time. Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 13, 2013 Share Posted February 13, 2013 Sounds like maybe the idle air control valve is stuck shut. Link to comment Share on other sites More sharing options...
GrimGreg Posted February 13, 2013 Author Share Posted February 13, 2013 Tonight I pulled off the intake and IACV and cleaned the TB and IACV. Started it up and it runs the same. Although one thing I forgot about was that it is only on the hot idle that the rpms are low. When it is first started it runs at 1100 RPM on cold idle. Link to comment Share on other sites More sharing options...
Precise1 Posted February 14, 2013 Share Posted February 14, 2013 Check out page 24 of ec in the FSM. I believe you are at the 'check EGR function' followed by 'perform OBD' step... B Link to comment Share on other sites More sharing options...
GrimGreg Posted February 14, 2013 Author Share Posted February 14, 2013 Well, my next plan was to start checking sensors with my multi-meter. I (surprisingly) do not have the FSM. Link to comment Share on other sites More sharing options...
Precise1 Posted February 14, 2013 Share Posted February 14, 2013 That should be easy to change? I didn't read all through it but it seemed like a sensible procedure, covering most of whats been said and going beyond. Let me know if you need a PDF emailed or something. B Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 14, 2013 Share Posted February 14, 2013 Sounds like it's got usual higher idle when cold, then it drops like it's supposed to (but goes too far). Mine had trouble with this a while back dropping too low and choking out at stoplights. Never did figure it out, but messing around with the TPS/MAF/airbox seemed to sort it out. Hasn't happened in about a year. Link to comment Share on other sites More sharing options...
GrimGreg Posted February 15, 2013 Author Share Posted February 15, 2013 What did you mess around with? Link to comment Share on other sites More sharing options...
Alkorahil Posted February 15, 2013 Share Posted February 15, 2013 Tonight I pulled off the intake and IACV and cleaned the TB and IACV. Started it up and it runs the same. Although one thing I forgot about was that it is only on the hot idle that the rpms are low. When it is first started it runs at 1100 RPM on cold idle. Just saw all of this...I was going with IACV as well.....hmmm What about the IACV regulator? Link to comment Share on other sites More sharing options...
Alkorahil Posted February 15, 2013 Share Posted February 15, 2013 Sounds like it's got usual higher idle when cold, then it drops like it's supposed to (but goes too far). Mine had trouble with this a while back dropping too low and choking out at stoplights. Never did figure it out, but messing around with the TPS/MAF/airbox seemed to sort it out. Hasn't happened in about a year. I looked at the FSM. Both the IACV and TPS have trouble shooting and diagnosis/testing proceedures for the hard parts that might be worth looking into. Also mentions bad/stuck Engine Temp Sensor to the ECU <- interesting!! There is also the idle speed adjustment screw, has it been messed with at all? If no it doesnt make sense to mess with that then. If vacuum lines are fine..... hmmmm. Secondary air system hoses under the intake plenum....are they good and not cracked? PCV valve clogged shut? If it is those hoses underneath are probably clogged too. Fuel pressure regulator vacuum hose from the back of the intake plenum to the fuel regulator. It is about 3-4 inches long right above #6 spark plug. It is prone to crack on the ends and leak the vacuum or simply fall off/come unattached. that would effect idle. trying to think outside the box here..... Link to comment Share on other sites More sharing options...
GrimGreg Posted February 15, 2013 Author Share Posted February 15, 2013 I had to pull the hose off the PCV valve to get to one of the IACV screws. I hit it with some intake cleaner while the hose was off, but didn't test if it was stuck. And I had the intake off to clean the TB. I'm running a custom straight pipe intake with the vacuum lines tapped into it. The pipe and joiner clamp areas were in good shape. I'll probably tear into it more this weekend. Link to comment Share on other sites More sharing options...
RF600 Posted February 17, 2013 Share Posted February 17, 2013 When my IACV was acting up it wouldn't hold an idle. I have heard that the MAS drops its ground sometimes. Mine was acting weird and I cleaned up the mas and no help. I put a new connector and added a ground for the MAS and I have not had a problem since. When the MAS would drop the ground the truck wouldn't hold an idle. I replaced the IACV first and the controller. All good for a while then I did the MAS connector and ground. So far so good. Not sure if that helps or not. Link to comment Share on other sites More sharing options...
GrimGreg Posted February 19, 2013 Author Share Posted February 19, 2013 Never had an issue myself (I guess yet...) with the MAF ground. I know it is a known common issue, and what the fix is. This weekend looks like it might be nice enough to allow me to tear into it and check my sensors. Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 20, 2013 Share Posted February 20, 2013 What did you mess around with? Mostly the airbox. Maybe there was a problem with the MAF harness that went away when I messed with it, maybe the accordion tube was sitting wrong and opening a crack... I still dunno what fixed it. It might have cleared up on its own, but my dad insists that messing with the airbox fixed the problem. I cleaned up the TPS and MAF after the fact just in case. I still don't know what caused the problem, only that it started when I left the lights on and drained the battery. Link to comment Share on other sites More sharing options...
GrimGreg Posted February 25, 2013 Author Share Posted February 25, 2013 Replaced the PCV valve and it got a little better. Adjusted the idle screw to get it where it should be after that. Link to comment Share on other sites More sharing options...
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