5 Bucks to Whoever Can Diagnose Rough Idle

Jason_25 · September 12, 2002

Ok I have checked it all.

I can feel the engine shake on the inside, I can watch in shake if I pop the hood, and I can even hear it and see it (just barely) on the tach.

Vacuum pressure is consistent and within specs, fuel pressure is within specs.

New MAF, plugs, wires, IAC, TPS, and oxygen sensors.

I have flushed the engine out with seafoam as well.

What Next?

410Fortune · September 12, 2002

spark plugs and fuel filter

how many miles on the truck?

SaleenEXP · September 12, 2002

for a rough idle I would definetley check the spark plugs and fuel filter first, thats what I do on our waverunners when they start running ruff and its always the plugs, but their not like a car, we have to replace the plugs ever 8-10hrs of time on them.

if your engine is shaking, thats not good, check the motor mounts.

Jason_25 · September 12, 2002

Its definitely not the motor mounts!

New spark plugs as mentioned above.

Fuel filter would not affect the engine at idle. It is not restricted at all. Revs freely to WOT. Gas mileage is good.

espnfreak · September 12, 2002

oh man, i read that and i was going to suggest motor mounts right off the bat....cuz thats what they said was causing all the vibrating on my moms 95 camry

410Fortune · September 12, 2002

How many miles? You can have the injectors cleaned professionally. Have you checked the lower intake bolts?

dogfriend · September 12, 2002

done a compression check lately?

It could be a burnt valve

hopefully not though

Jason_25 · September 12, 2002

Like I said Vacuum is perfectly within specs and is steady, so I don't suspect the intake manifold bolts. Plus I have never heard of any 95+ with loose intake manifolds.

I have considered injectors but would like to know for sure before I shell out the money for them.

The truck has 100K miles.

A BURNT VALVE!!!!! God I hope not.

section525 · September 12, 2002

How about coil packs, or the V6 equivilent. Thats what was wrong with mine. Felt like a big block in the drive-thru.

Jason_25 · September 12, 2002

I am unsure as to how to test the coil pack, and I doubt it has failed. I have never heard of the coil pack failing on any of the V6 explorers.

dogfriend · September 12, 2002

sorry, just a possibility

A had a 89 Ranger that had a rough idle, and a friend of mine said I probably had a burnt valve...he was just trying to annoy me though. If you had a burnt valve, it would likely show up on the vacuum gauge. A compression check would show it for sure.

I think an injector would be more likely, but the later models are supposed to have deposit resistent injectors. You could try one of the 'noid' lights to see if signal to all injectors is consistently even.

I never solved the problem on the 89 Ranger.

SaleenEXP · September 12, 2002

If everything else is fine, that I would definitley look at the valves. Are you sure it's not the motor mounts? Is it a serious shake or a vibration? cause I saw that you said the engine was shaking.

dogfriend · September 12, 2002

test coil pack

you test the coil pack by checking primary and secondary resistances with an ohmmeter. I doubt that this is the problem though.

Jason_25 · September 12, 2002

No it's not a serious shake at all. I can just see the motor moving and "feel" it in the seat and through the steering wheel.

410Fortune · September 12, 2002

Seems to me you are too quick to dismiss these suggestions. the Fuel filter sure can effect the idle. Just because your vacuum reading are coming up okay doesnt mean you dont have a loose lower intake or bad gasket.

Also what kind of plugs did you install? Have you checked the gap on each plug? Have you looked at each plug for the color? Usually a small miss like this at idle is something simple, like a loose wire boot, a dirty filter, a dirty MAS, or just a bad connection somewhere......

They can sure be a PITA to diagnose though!!!!!especially over the web!!!! keep at it and we'll get it....

Jason_25 · September 12, 2002

How can the fuel fliter affect idle? The engine needs almost no fuel at idle.

Also please explain how the intake manifold can be loose but yet the engine vacuum is within specs, I don't understand.

I used motorcraft platinums, and yes I did check the gap. The old plugs were white in color, most notably on the driver's side. #4 was the worst. Haynes manual says this signifies a lean condition. Wire boots are tight. The MAF is new, as in like 2 weeks old.

Also, I don't see how a dirty air filter could cause a miss either, unless it was totally clogged. Mine's just a little bit dirty.

410Fortune · September 12, 2002

The fuel pressure at idle is still 38#, injectors need the pressure to spray regardless of rpm, this is not a carbuerator.

I checked all my vacuum lines and system and it came within spec, however my lower intake bolts were finger tight, fixed that, high idle and loss of power intermittant problem dissapeared......How? I dont know, maybe it's where the leak is occuring, maybe it's where the test is being performed, just a little real world experience is all...

Is yours an EGR equipped engine?

What brand of 02 sensors did you use?

have you actually looked in your intake, throttle body, etc?

Have you hooked the little sucker up to a real scanner while the engine is running? monitor the 02's, the MAS, etc...?

You wouldnt think a fuel filter could effect idle, if everything works perfect at all other RPM's but I assure you the FRAM filter I had on my 2.9L gave me a terribly rough idle when it was on there for two weeks, ran perfectly otherwise.

I am guessing your miss is occuring at all times, it is just more noticable at idle.......

Dont rule out the EEC itself as the problem....

You can also have your exhaust flow checked...

Lean condition points us to:
02 sensor(s)
Fuel pump or filter
and most of all the pesky little fuel pressure regualtor

then the injectors, MAS and the computer itself.......

Jason_25 · September 12, 2002

410, I appreciate the input. My next step I suppose is to change the fuel filtter and take a look at those lower intake manifold bolts.

Yes, it has EGR.

Bosch o2's.

Yes I have looked in there. It is very clean.

It very well could be occuring at other times as well. Power could certainly be better. It also seems to have erratic performance.

One of the only things I haven't done is hook it up to a scanner.

Oh yeah, forgot to mention I put a new FPR in there too.

Broccoli1 · September 12, 2002

Check the Flux Capacitor

410Fortune · September 12, 2002

BOSCH!!! BOSCH!!!! YUK!!!!

Actually people have posted about this a hundered times, the Bosch 02's dont seem to work too well, however it is usually a problem with lasting long time, so if they are new it cant hurt to hook them up and test them but I doubt they are the problem.

If the performance is erattic at all times, I would FIRST check those bolts, then replace the friggin filter, they are VERY picky when it comes to fuel filters, I change my motocraft filter every year.

It could be many many things, you just have to go through the steps instead of tossing $$$ at it (fuel filters are cheap so that kind of stuff does not count!!)

Your EGR is probably clogged, that could do it for sure!! Seafoam may work good at getting some carbon loose but nothing is gonna free up a clogged EGR valve....

A scanner can help find this problem....

5 Bucks to Whoever Can Diagnose Rough Idle

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