Stumble at idle

[Primer88]

In the last couple weeks my 00 2.5L auto has had a slight to bad stumble at idle and more recently a stumble cruising at 50-60mph under light to moderate load. When it's happening the only common factor is the engine is running and it's at operating temp. Doesn't matter if the AC compressor is on or off and it also does it with the hvac switch turned to any position. I did a major tune up about 2 months ago which included wires, plugs, cleaned MAF, both O2 sensors, pcv, fuel filter, iac and I cleaned the entire intake and tb. I did all of that in one day and have put over 3000 miles on it since then without a problem. All the replacement parts were Motorcraft.

When it's stumbling the CEL doesn't even flicker and the transmission feels fine. I have checked all of the vacuum hoses for leaks as well. A couple of the hoses are cracked but don't seem to have any leaks.

It's never consistent (other than it only happens when the engine is warm) and mostly happens at idle. It can be just a hickup or start rockin like it's got a monster cam in it. Then engine never dies.

I unplugged the iac while it idling very rough and it seemed to even out pretty well, I also gave it some gas and the revs went back to idle fairly well but it never dies.

I have cleaned the MAF and IAT sensor with no change in the condition.

I put a fuel pressure gauge on it and it held rock steady at 68psi while idling fine and while it was idling rough.

Suggestions? I have never touched the EGR system or the coil packs. This truck has 134,000 miles on it as well, could this problem be a sign that the timing belt is about to break?

 

[Bryan22]

I would start by testing the coil packs with a multi meter, and make sure they're within spec.

 

[wally]

you may also want to try taking the vacuum hose off the egr and plugging it to see if that helps, if it does it may be the DPFE or the EGR valve.

 

[Primer88]

Thanks for the replies.

ok..............now it's not really having a problems at idle but it's having massive problems while driving. It has almost no power and is stumbling hard while driving in all load conditions and speeds. I ordered new coil packs the other day and they should be on my doorstep in a couple hours.

 

[Primer88]

Changed the coil packs and it seems to be purr'n like a kitten now.

 

[Primer88]

ok, the coil packs didn't fix it. I just changed the IAC again and no luck either. I unplugged the new iac while it was running as well and it didn't die. I unplugged most of the vacuum lines I could get to and plugged them, no change. I unplugged the hose from the EGR several times today and no change as well. All of the times I unplugged the vac line from the egr it wasn't pulling air anyway. I think I'm just going to take it to the shop at this point.

 

[wally]

May possibly be a timing issue, cam position sensor possibly? Haven't heard to many people having to replace them though

 

[fivestring]

Also, look at the CAT after driving a few miles and make sure it isn't glowing. CAT may be clogged up.

 

[Primer88]

Well, my truck has been at the Ford dealership for 9 hours now and they still don't know what is wrong with it. The only code showing in the computer is P1000 which apparently means that the computer had been cleared. It's been running like crap since the last time I unhooked the battery so whatever the hell is causing this isn't throwing any codes. They are "suspecting" that the timing belt has stretched and OF COURSE the damn truck hasn't had a single stumble or hiccup the whole time they have had it AND it didn't do it once when I drove it the 20 miles down there this morning. It ran like **** all day yesterday though.

The cats seem to be operating fine. The flow coming out of the tailpipe doesn't seem any different that before the issue started and they are definitely not even close to glowing.

 

[Rackster]

Stumbling

I was thinking you might have gotten a bad tank of gas, but it would have you bucking all the time.

 

[Primer88]

I was thinking you might have gotten a bad tank of gas, but it would have you bucking all the time.

I've gone through about 4 full tanks of gas from different gas stations since this problem started btw.

The dealership had it for 2 days and couldn't come up with anything. My girlfriend got in it and drove it while I was talking to the techs and the problem happened so she came back and took one of the techs for a ride. Of course......it didn't do it, and it only did it (slightly) to me once on the way home which is out of character for how it's been acting for the last couple weeks. They didn't charge me anything and said to drive it around for a while and make sure not to reset the computer so they can possibly grab some data off of there to find out what is wrong. The tech I spoke with suspects that the maf is bad. He thinks that it might be getting confused with what elevation above sea level it's at.

Another thing that has me confused is my sudden drop in gas mileage. Since I moved from Knoxville TN down here to northeast AL I've gone from a logged average of 21.58mpg down to 16.72mpg. When I first moved down here back in late April I started using the air conditioning and I bought a set of Goodyear Wranglers because my truck desperately needed new tires. I have since replaced those all terrain tires with a set of Firestone Firehawks which I had on my last 2000 Ranger (4.0L). That along with the major tune-up and e-fan install I did back in early June didn't help the mileage at all. My driving style and type of driving I do hasn't changed since I moved down here. I didn't keep very good track of my mileage last year but I always calculated it at every fill up. Even last summer when I used the AC it didn't kill my mileage and the only difference with that system from last year is I recharged the system so it actually blows cold now. Hell, even when I moved down here I managed 19.7mpg towing a 2000lb trailer.

 

[Sunk]

Mine's in the shop right now, for something similar. It stumbles when coming down to idle from higher RPMs. They've checked everything (so have I) and they're leaning towards the computer.I had a couple injectors replaced like 5-6 months ago and they said it was the computer too.

This shop said they hadn't replaced the MAF since it was expensive, but they're working on that now. If it doesn't work, I won't be charged.

 

[Rackster]

Stumbling

We had a somewhat localized issue here in Connecticut a few weeks back where a few bad deliveries of fuel loused up a bunch of folks cars. But that said, I agree that your buying a few tankfulls and the randomness and severity of your events are probably not fuel related. I also think that if it were electrical (i.e. coils, plugs, or wires) in nature, the symptoms would be consistent and worsen with time. I guess it would have me leaning towards a sensor issue as has been noted here, or perhaps a failing IC that gets hot and starts to intermittently fail (or is affected by a temperature range). A computer that is bugging out could be at the root of your fuel efficiency dropoff.

Have you noticed environmental factors that are present when the symptoms strike? For example, certain humidity or temperature range? Before, after, during rain? Can you ascertain if any of these exacerbate the situation? Perhaps occurring more at dusk and/or dawn? Just shooting from the hip here. Also, you might want to check out if there is/are service bulletins for this type of problem.

Kevin

 

[Primer88]

Have you noticed environmental factors that are present when the symptoms strike? For example, certain humidity or temperature range? Before, after, during rain? Can you ascertain if any of these exacerbate the situation? Perhaps occurring more at dusk and/or dawn? Just shooting from the hip here. Also, you might want to check out if there is/are service bulletins for this type of problem.

Kevin

The issue happens at all engine temps, outside temps (and humidity), night and day. At the beginning the only common factor was the engine being at operating temperature. Then quickly progressed to whenever it wants to. I am very analytical and I take note of when odd things happen or something is out of place. At this point, the only common factor with this problem is that the engine is running. Any gear, any speed, all positions of the HVAC, any radio station. Only time it's never done it to the point where I can notice it is at WOT.

 

[Rackster]

The issue happens at all engine temps, outside temps (and humidity), night and day. At the beginning the only common factor was the engine being at operating temperature. Then quickly progressed to whenever it wants to. I am very analytical and I take note of when odd things happen or something is out of place. At this point, the only common factor with this problem is that the engine is running. Any gear, any speed, all positions of the HVAC, any radio station. Only time it's never done it to the point where I can notice it is at WOT.

Good analytical skills are going to help! So, it sounds like we can begin to rule out environmental factors that can change an electronic component into a semiconductor. Underhood temperatures keep things a bit more consistent. So many new electrical parts, so assuming that the spark is there. Clean fuel and cleaned throttlebody so assuming that's o.k. to. New O2 sensors (and filter?), so it's probably breathing right. So you are getting all three components for combustion.

Wally may be on to something (along with the Ford techs). The timing belt may have stretched or is loose. I don't know how negatively the timing is affected if you skip a tooth on the belt, but as you get further away from optimal, fuel efficiency and power are affected. I had a tensioner issue with an old Nissan Stanza. I heard the timing chain rattle and as I drove, it would skip a link and bog the engine down, but then jump back a tooth and drive normally. I didn't know what was going on immediately, but then I found out the hardway. I had it repaired and 20K miles later, it threw the chain again (culprit: cracked crank sprocket rotating slowly on the crankshaft). Same symptoms on the second event, and was within 1/4 mile of my house when it happened (as I came to the last stop sign).

When was the belt last changed?