Please Help with Rough Idle

[bpopp]

Please Help with Rough Idle - Solved

I have a 99 Ford Explorer w/ the SOHC engine and 110k miles. This is my second engine (first was cooked by notorious timing chain tensioner). The engine was running great when my auto transmission went out about a month ago. The cause of the transmissions demise was most likely a wiring harness getting busted up and coming loose enroute. I got a big jolt shifting into 3rd and a blinking OD light. Had the transmission replaced w/ a junker and they rewired the harness. They also replaced the AC compressor (so I have air now).

Unfortunately, now I have a very rough idle (wasn't there prior to transmission failure). Here's what I've done/noticed:

* Idle bounces between 400 RPM and 1400 RPM every 2 or 3 seconds. On the low end, it shudders and shakes the entire truck.
* Have DTC P0171 and P0174 (lean bank 1 & 2)
* If I unplug the MAF, my idle clears up substantially. I cleaned it w/ electronic parts cleaner, but this didn't seem to make any difference.
* I also replaced the MAF w/ a new one, but as soon as I plugged the new MAF in, rough idle returned. Unfortunately I did not think to reset the computer before removing and returning the new MAF.
* The idle is only rough in Park and Neutral. In drive or reverse it clears up substantially. Still not perfect, but the bouncing/shuddering goes away.
* Replaced the DPFE/IAC w/ parts found at a local junkyard. They obviously aren't guaranteed to work, but made no discernible difference.
* Checked the fuel pressure and it's around 60PSI.
* Tried using propane to search for a vacuum leak. Couldn't find one.
* Don't hear the notorious death rattle yet, but it's been very warm here.
* Rough idle exists even w/ the AC turned off.
* Idle does not improve or degrade as the car warms up.
* Engine runs okay at higher RPMS, but it seems weak on inclines and doesn't seem to have the power it did a month ago.

I tried taking it back to my mechanic. He said he was getting a misfire on a couple cylinders. Changed a few plugs out and said it was fixed. He also said that one of the injectors was "acting funny" and that I should run some injector cleaner through it (which I did). The CEL was still on and it didn't seem any better.

He assured me it was nothing he did, but I'm wondering if he possibly switched a couple wires around when he was wiring that harness back up (it's the harness that connects the transmission to the computer). I think there's also an oxygen sensor back there that connects into the same bunch of wires. Unfortunately it's on top of the transmission so I think it would be very hard to get to without dropping the transmission.

Anyone have any ideas? I'm ready to light this b**** on fire. I love my Explorer, but this is so frustrating and I'm worried it's going to damage the engine having it running so rough.

I have a crappy scanner, but am contemplating buying a OBDII Automotive Scan Tool to see if I can get a little more information to work with. There are about 10 different causes listed under the DTC of "lean bank".

 

[TheJackal]

All you need to get are the OBDII codes (the numbers themselves, usually with a P in front). If you post them, we can tell you what they mean.

A misfire can be caused by bad plugs, bad wires, coil pack, cylinder compression, injector failure, or a few other reasons.

 

[chance942]

Are you reading the fuel psi when it's jumping around at idle???

 

[bpopp]

Only codes last time I checked were P0171 and P0172 (lean bank 1 & 2). I checked the fuel pressure with the ignition off and it was 60PSI. I didn't crank it because my dad rigged a gauge out of shop parts and it wasn't sealing very well. I'll pickup another gauge and try it again running. The thing that makes me think it's not fuel related, though, is that it only happens in park and neutral. In reverse or drive, even without applying gas, the idle is relatively smooth (about 600RPM).

 

[chance942]

I hear you man. They frustrate the hell out ya. I know I've beat the fuel thing like a dead horse but only out of expierience. If you can spend the cash get the better scanner. Does your dad have any cars he could use it on? I'm guessing yes. Maybe you guys could add it to the shop. I broke down and bought the $140 or so one from Autozone and it has paid for itself. Not on my EX because as you say lean 1 and 2 is so freakin vague. I've fixed some other cars with info from it so I'm happy. The reason I recommend it for you is that it will monitor your o2s and a lot more.

Let's see I've got the Actron model CP9175.. It has freeze frame data,I/M monitors and code look up on it.

Okay do you have a fuel return line? How long after you turn it off is it holding 60psi? I got a fuel gauge at Harbor Frieght that works fine for as much as I've needed it(not much). It does have the connector you need for the schrader valve though,it's kind of a PITA to connect but it works. If you could read it when it's doing that with a leak free gauge that'd be awesome.

Now admittedly I'm not an auto trans guy but I believe a bad running engine on these makes the tranny do funny things right? I can't explain why it would even out to 600rpm in D or R. How much does it fluctuate away from 600? In drive if you hit the gas what does it do? Do you have this problem all the time? You mentioned it being hot outside. Anyway man I hope I can help ya'll out. I know exactly how you feel.

 

[bpopp]

When it's in park or neutral, it fluctuates a lot. It jumps from around 1300-1500 back down to under 400. Obviously when it gets on the low end, it starts sputtering and vibrating (sounds very unhealthy), and then something kicks in and it revs back up to 1300+, sits there for a few seconds (running fine), and then starts dropping back down towards 400. As soon as I shift it into gear, it slowly drops back down to 600 or so and sits constant. Even then, the idle doesn't sound perfect, but it's much more acceptable. From what I've read, this sounds like the IAC, but I've cleaned it, checked it (voltage and resistance are right), and even replaced it with a junker IAC, and it didn't seem to make any difference.

 

[cdg2000c5]

i have a 98 with the rough idle and lean codes.. i believe mine is due to a leaking intake gasket (mine is leaking coolant).. might wanna replaced your gaskets.. i'll post results as soon as i finish

 

[bpopp]

Yeah, that's on my list. I don't think that's it, though, because mine doesn't improve as the engine warms up. I've used a propane bottle to go around the lower intake and I don't get an RPM boost. I also wouldn't expect an IM leak to improve once you put it in gear.

A coworker is going to bring in a fuel gauge tomorrow. If that doesn't pinpoint anything, I may just take it over to a dealer and ask them to troubleshoot it for me. I feel like my problem has to be electrical.

Thanks for all the suggestions.. please keep them coming.

 

[chance942]

I don't see how coolant could be leaking into the manifold through these gaskets(upper and lower) atleast not on a 99 0r mine(2000). Before you take it to a dealer call the service department. Ask to talk to a service advisor. They won't have a clue how to answer your question so be real nice and ask if there is anyone who might be able to do so. If that person doesn't know,do the same thing,just be nice. You have enough information from what I've read and if you relay this someone WILL talk to you about it. As long as you're are courteous and relay the knowledge you've posted here I believe you might get some good insight. Don't be afraid to call many dealers,if one is rude or not helpful call another. I've done this and solved an IAT issue by tracing wires from the pinholes from the PCM while on the phone recieving instructions from the shop foreman.

Just something to consider before you go and pay $85/hr for a novice tech to find nothing and pass it up to the foreman anyway.

Like I say man try many dealers if you have to. I know which dealership I'll buy from without a doubt if I ever need a part or a car. That dealer is 40 miles away and I'll go there before I go to the one that is 4 miles away.

 

[bpopp]

Chance, bud, I think I owe you a beer. You might have been dead-on. I still don't have a fuel gauge but tonight I went up and bought the quick-release tool to change out my fuel filter.

The fuel coming out of the filter was a dirty brown color, but not altogether horrible. I cranked it up not really expecting any change and after it got some fuel, I quickly noticed that the idle had smoothed out substantially. It's still rough, but it's not bouncing all over the place like it was. And while I was back there checking for fuel leaks, I heard a buzzing sound coming from the fuel pump. It might have always been like that, but it sounded to me like a bad motor.

A coworker is bringing me a fuel pressure gauge tomorrow so I'm hopeful that that will confirm what you suspected all along.

/fingers crossed

 

[chance942]

Right on. When I changed mine it was that brown color too. From what I've learned you're only supposed to hear a "humm" from the pump right after you start it. So hopefully you're right about it being fried. It isn't that bad to change,ofcourse if you empty it out as much as possible. You'll need the tool,which you have and hopefully pops will help out. Good luck.Let me know what happens bud.

 

[cdg2000c5]

mine was idling rough in neutral and in gear.. i don't think that really matters.i removed the upper & lower IM last night and it was definitely the coolant leak culprit. just thought i'd mention it

 

[chance942]

So you had coolant leaking in through a bad o ring or what?

 

[cdg2000c5]

it's leaking out.. down the front side near the water pump.. i had a pool of coolant in the valley between the intake ports on my heads

 

[chance942]

oh that's sh*tty man,sorry. so it was leaking in through an o ring on a runner(s). Is your pump going out or a gasket leak?

 

[bpopp]

Well, the good news is that I've ruled out fuel as a possible cause. The bad news is I still have my rough idle. I bought a gauge at harborfreight. It registered about 40psi before I turned the car on. 60 with the key to on, and about the same with the engine running. It was a steady needle and there was very little bleed when I turned the car off. Seems everything is order on that front.

I bought the intake gasket kit, some new plugs, and new wires and am going to swap them out tomorrow. That will rule out everything except a vacuum leak in one of my hoses, bad injectors, or a timing issue. Wish me luck.

 

[chance942]

Yeah sure hope it's not the damn timing issue. Good luck.

 

[cdg2000c5]

well i replaced my upper and lower IM gaskets and i tossed a new 180 degree thermostat in mine and so far so good.. the idle is smooth once again and so far i havn't located any leaking.. time will tell though as far as the leaks go.. i sure as hell hope it's not a head gasket..

 

[chance942]

Yeah never good to have a leak with an unknown source. You couldn't tell where it was coming from while you had it apart? Damn that ain't good.

Hope your gasket change does the same for POPP.

 

[bpopp]

Well, just finished the upper and lower intake gaskets. It was fun, but no joy. It's still idling rough. I'm getting desperate. I don't have much left to try. Tomorrow I'm going to change the plugs/wires. If that doesn't work, I think I'm gonna have to break down and take it someone.