92 rough idle

dinosore · Mar 16, 2014

Hey all. My engine has had a rough idle for a little while now. It was not enough to bother me really. But I would like this truck to last. I started at the basic points. Cleaned the MAF, IAC, and Throttle body. New air filter. No vaccum leaks that I can find. Seafoam through the brake booster, and oil ( then changed oil after a run to the desert and back). After all that it still had a rough idle but not as bad , a couple days later it went back to how rough it was prior to all that. No CEL light. drives well just idles rough.

I don't know how to explain these sounds but I will try. There is almost a glub/bubble sound when idling. In words its kind of like... hum hum hum hum hum hum hum hum glub. When I unplug the MAF it still idles rough but that glub/bubble sound disappears. Secondly I cant catch the timing of the "ping" to describe it but it seems as if the engine goes through two cycles of idling then I hear a "ping" which I thought could be a valve hitting...idk

Where do I go from here?

Ps I pre-thank you to all those for posting "time for a 4.0" to which I respond I wish I had the time, space, and money. But a 4.0 won't happen till this 3.0 is dead

Rearanger · Mar 16, 2014

dinosore said:
Where do I go from here?

Compression test (hot engine). Ohm test ignition wires. Inspect plugs.

RonD · Mar 16, 2014

I would change the spark plugs.

I would try some Seafoam in the fuel tank, to clean injector tips.
At idle the air velocity in the intake is the lowest, an injector with a dirty tip will drip fuel instead of spraying it, this can cause a lean mix in one cylinder, this can cause a miss and a "ping" noise from lean mix pre-igniting during compression.
At higher RPMs the air velocity causes dripping fuel to go into vapor form more easily, so less noticeable but could still get a "ping" now and then because fuel/air would still be a bit lean.

If you have an EGR system the EGR valve can get dirty and stick open a bit, this will foul up air/fuel mix at idle but not be noticed at higher RPMs

dinosore · May 4, 2014

Okay so I performed a compression test. my readings from back rear right of the engine in a clockwise motion are 110/110/100/110/110/105. I changed my plugs and wires, although my plugs looked good when I pulled them but it was only 20 bucks for motorcraft platinums so i figured why not. I'd say no change in my idle...possibly a little rougher now actually. It isn't super rough but you feel the wiggle at a red light. I verified my wire order from dist. to plugs. I know there are different length wires and I measured the new ones to old ones in a one by one fashion, meaning all wires were connected to the plugs and id pull one wire change the plug measure it up to the new wire and replace it, then moved on to the next. Where do I go from here in terms of getting to idle without feeling it in the cab?

RonD · May 4, 2014

Did you have all the spark plugs removed when you did the test?

The numbers show there is not one cylinder that is bad, i.e. a burnt valve or other cylinder leak, but...................

You would expect 150+ psi/cylinder on that engine even cold with throttle plate closed, any engine really, that has 9.0:1 compression ratio.
Failing timing chain tensioner would lower compression across all cylinders, but so would a low battery or uncalibrated pressure gauge

Loose timing chain would make a noise, a metal rattling noise from front of engine

dinosore · May 4, 2014

all plugs were out at time of compression test. tool was rented from autozone so can't comment on claibration of the tool. no rattling from the engine so doubt the chain. When I cranked the engine for 5 cycles with no throttle open on an engine that ran parked and idleing for about 5-10 minutes.my temp gauge had barely moved but it takes a long drive to get the temp going...sometimes about 15 minutes before it moves.

Rearanger · May 5, 2014

Do you have EGR?

Rearanger · May 5, 2014

dinosore said:
When I cranked the engine for 5 cycles with no throttle open

That may explain low compression numbers. Why 5 cycles? WOT, crank until max psi. Hot engine better.

dinosore · May 5, 2014

yes i have an egr. i cranked 5 cycles cause that way i knew I cranked each cylinder the same amount incase my numbers implied a problem. I know the hot engine is better so i let it run idleing while parked...but i only have street parking and it was sunday so if i took the truck for a drive i'd likely lose my parking spot.

Rearanger · May 5, 2014

Remove and clean EGR valve and check vacuum operation. If it does not close completely (minor leak due to crud) it is a vacuum leak. Major leak will stall engine at idle.

Rearanger · May 5, 2014

Also check ignition wire resistance.

dinosore · Jul 17, 2014

EGR was cleaned...then replaced a few weeks later just to be sure. Wire resistance was good all the way around. spark plugs are properly gaped. The rough idle i feel is a shaking of the truck. after doing all the work discussed in the thread it is still there. I checked my motor mounts but don't see anything visible wrong. When i open the throttle plate the drive side of the engine lifts but and tilts to the passenger. I opened the throttle while watching both motor mounts and don't see any noticeable movement from either. Is there a chance it could still be the mounts?

Rearanger · Jul 18, 2014

How many miles on this truck?

dinosore · Jul 19, 2014

the odometer says 11xxx.x because thats all it has space for so 111xxx, 211xxx,311xxx? your gues is as good as mine really. Truck was owned by a nice ederly man before I bought it. His wife sold me the truck after he passed an said it was 102,000 but who knows for sure...and yes ive only put 9000 miles on the truck in two years, it is my climbing/camping rig

Rearanger · Jul 19, 2014

Odometer should be able to go 999,999. I'd say the 102K when you got it should have been right. If true that's not many miles. If the miles are that low I'd want to put some money into the truck. You've done a lot of work on the rough idle.

You may want to consider sending the injectors out for test/clean. About $15-$20 per injector with your labor. Otherwise maybe just live with the idle.

That 105 psi cylinder is low, but not really when compared with the others. You should have just kept turning the engine until max psi reached, that would give you a better idea on the 105 cylinder. Next question is if that cylinder is unduly low what do you want to spend to fix??? Could be a lot of money.

92 rough idle

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