Erratic idle on startup [Archive] - Jeep Commander Forums: Jeep Commander Forum

: Erratic idle on startup


kriminaal
09-14-2011, 07:01 PM
I was pretty sure I found some threads on this a month ago but now can't locate them. Can anyone find them for me?
When I start up cold the rpm's bounce up and down erratically until it's warmed up and then it drops as usual.

rhobll
09-15-2011, 10:30 AM
Yes. My 2006 3.7 does this. If I try to pull out during this erratic idling, it'll try to stall, never does, and have no power. If I let it warm up 25, 30 secs, everything's fine. I've been living with this only because there are no codes thrown, and I know i'll be shelling out endless amounts of $, and no solution.

kriminaal
09-15-2011, 10:40 AM
Same as my 06 4.7L.
I have seen some possible issues but can't recall where I found them. Now that I have a service manual I was gonna tackle it. But can't find the possible solutions again. grrrrr

rhobll
09-15-2011, 10:46 AM
There was some mention about spark plugs. I think if they were suspect, the problem wouldn't go away in such a short period of time. For the record, I run the NKG Iridium 9, which are not stock.

Mongo
09-15-2011, 03:15 PM
1. Check for stored fault codes, see the sticky about the key dance to read them out on the EVIC.

2. Check all your "periodic maintenance items", some people still call it "tune-up" items, if you are due soon or overdue, these things cause poor idle. Like Spark Plugs, Ignition Cables, Air Filters, PCV Valves.

3. Put some Fuel Injector Cleaner in the Tank, I've "heard" Chevron, with "Techron" is the best at cleaning the injectors.

EGR, check it, I've had bad EGR's cause my idle to surge up and down, but it did it warm and cold. Plus, some engines don't have an EGR and the Commander engines very well might NOT have an EGR.

AFA non-OEM Spark Plugs. The new DIS (Distributorless Ignition Systems) can do some funky things, like share 2 plugs between one coil, and run one of the two plugs with reverse current. As well, they can be more sensative. The recommended plugs are the ones that have been tested with your engine and proven to work. NOT necessarily does that mean other plugs won't work as well, but if they are NOT recommended, then you just don't know.

Using Single Platinum/Iridium plugs with an ignition system that uses reverse current on half the plugs, you reverse anode and cathode on that plug. The whole reason Single Platinum/Iridium plugs last longer is because the harder metal on one electrode cause less metal tranfer during use. You reverse that, then you have faster metal transfer from the softer metal eltrode to the harder.

The Double Platinum Plug makers have all sorts of literature describing this and state this is exactly why they created double platinum plugs, i.e. platinum on both eletrodes, for the plugs that have reverse current flowing through them.

If I was having idle problems, and used something other than the recommended spark plugs, I'd switch back to the recommended plugs and see if that fixes it. It often does, but keep in mind, more than bad plugs can cause idle problems.

kriminaal
09-15-2011, 03:22 PM
Thanks, it is the plugs I'm beginning to wonder about. As I know I had my mechanic put in some high quality ones at 100k service.

samwise70
09-15-2011, 04:06 PM
I had the same problem earlier this year. I pulled my Idle air control off of the throttle body and cleaned it. It had a good enough build up of carbon that the seat wouldnt completely close. I took carb cleaner and a fine pic to gently scrape off the build up. don't damage the seat or you'll be buying a new one. It is easily cleaned.

Sam

Gulf550
09-15-2011, 05:36 PM
I had the same problem. It started off as just erratic RPM on strartup then after it warmed up it would be fine. After a few months, it got to the point any time I stopped my RPMs were jumping all over. I changed the throttle position switch, purchased from autozone, problem is fixed.

rhobll
09-16-2011, 06:16 AM
Thanks all, good info. Will report back after a few remedies are tried.

Trax95008
09-16-2011, 09:10 AM
my first thought was throttle body. it probably needs to be cleaned. when the throttle valve is closed, there is a small gap of air to idle. you get build up there blocking the air which is choking it so the computer gives it a little bit of throttle to keep it from dying which is when you hear it rev up. the computer then senses that the throttle position is too high for idle, and backs it off. that cycle keeps happening over and over, hence the reving up and down. so check your throttle body. if nothing else to eliminate that scenario.

kriminaal
09-19-2011, 10:07 AM
I haven't looked into anything yet but thanks for the replies.
I've been trying something out. Making sure that my fan is not on when I start it up. So far it has made a difference and is not doing the revving idle thing.

Mongo
09-19-2011, 01:15 PM
my first thought was throttle body. it probably needs to be cleaned. when the throttle valve is closed, there is a small gap of air to idle. you get build up there blocking the air which is choking it so the computer gives it a little bit of throttle to keep it from dying which is when you hear it rev up. the computer then senses that the throttle position is too high for idle, and backs it off. that cycle keeps happening over and over, hence the reving up and down. so check your throttle body. if nothing else to eliminate that scenario.
Depending on the year and the engine, you may have a Drive-By-Wire (DBW) Throttle Body (TB) or an old mechanical TB.

The mechanical TB will have the Idle Air Circuit motor and valve, that prevous posters mentioned removing and cleaning. The butterfly closes completely, and the idle air is routed around it controlled by the motor and valve. If the butterfly doesnt' fully close, that could be the problem as well.

The DBW TB has NO Idle Air Circuit, it merely cracks the butterfly valve to idle the motor. I guess dirt in the area where it cracks open could cause a problem like the old mechanical system. Some people have forced the butterfly open to clean it thoroughly, I don't trust that, I just pull the connector and 4 bolts to pull it off and clean it from both sides.