| Author | Message | ||
     John A. Addison (John_addison) New Member Username: John_addison Post Number: 1 Registered: 09-2003 |
I have a 1995 with a 3.9 V-8. It has a rough idle. This has gone on for a while. I have run fuel cleaner through it, but it is not any better. It doesn't seem able to keep the revs at 750 rpm. Now it is taking a long time to start (about 7 seconds of cranking). I have checked the compression and spark. Both are good. I think it is the fuel system. Does anyone know a way to test the idle air valve? Does anyone have any idea what it could be and how to test for it? | ||
| Phillip Perkinson (Rover4x4) Senior Member Username: Rover4x4 Post Number: 463 Registered: 02-2003 |
replace your fuel filter. I think the idle air valve is AKA stepper motor? there is some info on that thing in the tech section and I know it has been disscussed before try searching the archivse. you ever replace the fuel filter? whats the milage? | ||
| John A. Addison (John_addison) New Member Username: John_addison Post Number: 2 Registered: 09-2003 |
I have replaced the filter twice - no luck. The truck has 93,000 miles on it. I'll start checking the archives now. | ||
| Geoff 93 RRC (Geoff) Member Username: Geoff Post Number: 104 Registered: 11-2002 |
The stepper motor symptoms are high idle or too low idle, sometimes alternating between the extremes. Rough idle (like a shaking motor) is usually spark or vacuum related in my experience. If you are in the US the injector cleaner in all gas grades is pretty good (required by law), so I would concentrate on the other stuff first. Check that the distributor cap and rotor are not pitted, the plug wires are good. Look at an idling motor at night with no lights and see if you see any arcing from the plug wires. Tune-ups are due at 30K intervals (I do mine as needed so check manual). Don't pull the rotor off without applying opposite pressure at the shaft base with a screwdriver or something similar or you'll break the plastic retaining cap in the shaft. The plastic cap keeps shaft in place so that the counter weights and other internal stuff don't shift. If has been broken in the past its possible the rotor is moving around and not holding time correctly. It should move clockwise about 10 degrees under spring loaded tension. Make sure the wire harness from the alternator is tied as far as possible away from the distributor and any ignition leads as possible. Check that all vacuum hoses and connections are good. Replace the "emissions T" connector from the big breather on the valve cover to the intake plenum, or at least check that its not clogged. Some people have found the "air gap" between the magnetic rotor and the pickup inside the distributor gets out of spec. This can wreck idle big time. Don't have the gap specs with me - do a search for air gap. Is the ignition timing correct? The list goes on, but those are the usual suspects. | ||
| DiscoDon (Discodon) New Member Username: Discodon Post Number: 27 Registered: 08-2003 |
what about this one then.... Idle fine, motor drives really well but when coming to a stop after prolonged faster driving (70mph) idle sits at 1500 for about 30 seconds. | ||
| Chris Browne (Chris_browne) Senior Member Username: Chris_browne Post Number: 355 Registered: 02-2003 |
Stepper motor Discodon....its leting air into the injection system when extra isn't needed | ||
| DiscoDon (Discodon) New Member Username: Discodon Post Number: 28 Registered: 08-2003 |
cool, thanks. | ||
| John A. Addison (John_addison) New Member Username: John_addison Post Number: 3 Registered: 09-2003 |
This is very good advice. I have checked my distributor and it seems in good shape. I have just replaced all spark plugs and wiring. I will check the air gap. I have a copy of the specs on that. Reading the above correspondance and thinking about the way my idle is behaving, it sounds most likely to be the stepper motor. Would this also explain the long crank prior to starting? | ||
| John A. Addison (John_addison) New Member Username: John_addison Post Number: 5 Registered: 09-2003 |
Update: I purchased a fuel pressure test gauge and discovered that my fuel pressure decreases promptly after shutting off the ignition. The #2 piston injector is leaking. I found this by cranking the engine until it tried to start (~10 seconds). Then I removed the spark plugs and looked for the wet one. This also accounts for the smelly exhaust just after starting. I ordered an new injector from Atlantic british. i'll let you know how it goes. | ||
| Jared Schnelle (Jared) Member Username: Jared Post Number: 180 Registered: 09-2002 |
John, I paid 88 bucks to Rich at cruzinperformance.com and he serviced all of my injectors. I had 2 injectors which failed the leak test, but after he replaced the screens and pintle caps, where he also cleaned them in a supersonic bath, my idle was much smoother. I also took this time to clean out my plenum chamber, and stepper motor, since I had it all apart. |
