99 Explorer Idle Trouble

[goahunter]

Hi all,

I have been battling with my car for almost 3 weeks now. It is a '99 Explorer with the 4.0L SOHC. Upon cold start it is very erratic and bounces between 600 and 800 rpm. If the engine is warm it runs perfectly fine with no problems. I just got it back from the dealership but the idiots there did absolutely nothing to fix my problem after spending $$$. Im getting very tired of this and hope you guys can help. I have replaced the EGR, crankshaft position sensor, spark plugs, cleaned the IAC, checked the MAF, cleaned the TB, and new fuel filter. The dealer also replaced the vehicle speed sensor (I have no idea why). The car has 156k miles on it. It runs mobile1 5w-30 full synthetic. I have also run a minor amount of seafoam through it to see if that helps without any success. Any information would be greatly appreciated!

Thanks!

 

[2000StreetRod]

I've just started having similar symptoms. I suspect it is the Idle Air Control (IAC) valve. The first thing I'll try is to check the OBD-II trouble code for PO505 (IAC valve system fault). Then I'll check the resistance between the IAC valve terminals with the wiring harness connector removed. My Haynes manual specifies 6.0 to 13.0 ohms. I've had as many as three Volvos at one time in the past and always had a spare IAC valve on hand. High use electrically controlled mechanical devices don't seem reliable after five years or so.

 

[Fabbed4d88]

I have cleaned the IAC on my truck about 3 times...it helped a little but when I finally decided to replace it ........made a world of difference.

 

[mikepier]

Hi all,

I have been battling with my car for almost 3 weeks now. It is a '99 Explorer with the 4.0L SOHC. Upon cold start it is very erratic and bounces between 600 and 800 rpm. If the engine is warm it runs perfectly fine with no problems. I just got it back from the dealership but the idiots there did absolutely nothing to fix my problem after spending $$$. Im getting very tired of this and hope you guys can help. I have replaced the EGR, crankshaft position sensor, spark plugs, cleaned the IAC, checked the MAF, cleaned the TB, and new fuel filter. The dealer also replaced the vehicle speed sensor (I have no idea why). The car has 156k miles on it. It runs mobile1 5w-30 full synthetic. I have also run a minor amount of seafoam through it to see if that helps without any success. Any information would be greatly appreciated!

Thanks!

Sounds like the upper intake gasket problems. There was a TSB on the issue. It runs rough cold, but when warmed up and the gaskets expand, its fine.

 

[Dilbert5]

Check to see if the intake is leaking, take a propane torch (do not light it) and check the intake maniflod. If there is a leak, the propane will make a noticable difference in the idle.

 

[gijoecam]

My money is on the 00M12 lower intake manifold gasket set leaking. The problem eventually happens to all 4.0 SOHC's, but takes a lot longer to turn up in warmer climates.

Simple fix, $35 for parts and an afternoon under the hood.

 

[goahunter]

Thanks all for the posts, I changed the gaskets and the problem is no where near as bad, I can actually drive my car without fear of getting stuck somewhere. I still have a rough idle problem but its not as persistant. It now is very clear that It has very poor throttle response. Sitting at a red light today when the light turned green and started acceling the card practically died. Usually it is slightly delayed. I have noticed that when the car is rough idleing it almost smells as if it is running rich. Any ideas? friend told me it sounds almost like the TPS, could this be the problem?

 

[celly]

Have you tried Seafoam Motor Treatment? I had a similar issue in my old SOHC equipped Sport and a good fuel system treatment solved it. I didn't know about Seafoam back then but wished I did. I ended up paying someone to do a fuel system treatment for me. I don't put a lot of stock in most treatments out there, but swear by Seafoam (as do many others on the site).

 

[goahunter]

ya i ran a bottle through it about a month ago it fouled the plugs so i had to replace them when i replaces the intake manifold gaskets. seafoam just seamed to exacerbate the problem.

 

[goahunter]

i just replaced the iac and the tps, neither one did the trick. any other ideas?

 

[robertoa1a]

The dealer is only interested in selling you a new car.

Try cleaning the MAF and IAC with a safe cleaning spray. Replace the EGR valve. This should cost about $10. One guy found a dead bug on his MAF element after spending $400+ on unnecessary parts.

 

[goahunter]

k thx will try the maf next, im really running out of ideas, haynes manual isn't to much help now either

 

[robertoa1a]

That MAF is real sensitive to dust and plays the biggest role in drive-ability. It has heating like elements on it and it measures the air that passes through it then that data goes to the PCM where every thing else relies on that data. More than half or these issues are MAF cleaning issues.

If thats not it I would see if there is a timing problem.

 

[goahunter]

any recommendations on how to clean the maf? i know they sell a cleaner at autozone but anything else, i know your not supposed to touch the filament.

 

[celly]

any recommendations on how to clean the maf? i know they sell a cleaner at autozone but anything else, i know your not supposed to touch the filament.

Just spray the elements liberally and let it dry. That's about it. You're right. Never touch the filament.

 

[goahunter]

cleaned the maf really good let it dry for about an hour, replaced the gasket old one was a little flat. still same problem. Problem doesn't seem to be as bad but still exists. Used a whole can of MAF cleaner on the thing. Any new ideas?

 

[chance942]

fuel pressure?

 

[ERUSH97XLT]

Hi,

Rough Idles are a real PITA to diagnose, as I've experienced. It seems you've instinctively done what most would do; however, here's my two cents:

1. Check Vacuum. There could possibly be a smaller leak elsewhere.
2. Check Ignition Components: Sparkplugs, wires, coil, etc. A fouled plug or a worn wire can cause annoying problems.
3. Check Compression.
4. Check Fuel pressure.
5. Reset your computer after cleaning/replacing electronics by pulling the fuse or disconnecting the battery.
6. Are there any codes?

I haven't read the previous posts in detail; I just skimmed. So, I apologize if I'm being repetitive.

Let me know what you come up with.

Good Luck!

ERUSH

 

[ERUSH97XLT]

Oh, one more thing:

Since you said it smelled like it was running rich, the engine may think it's running lean; thus, it's trying to correct this condition by dumping lots of fuel in the combstion chamber. How's your fuel economy?

If the engine may think it's running lean, there are three possibilites which might be causing the problem:

1. Unmetered/falsely metered air entering the engine: Clean/Replace MAF and check for vacuum leaks. Even though you've cleaned the MAF, it may have failed, rendering the cleaning ineffective.

2. Oxygen sensors: If the MAF and Vacuum issues have been fixed/ruled out, these may be faulty, as they are incorrectly informing the engine there is oxygen in the exhaust, causing excess fuel to be injected.

3. Poor ignition: Unconsumed oxygen from poor/no combustion is picked up by the oxygen sensors and registering as a lean condition, causing excessive fuel enrichment. Check you plugs again, wires, and coilpack.

What does everyone else think?

ERUSH

 

[robertoa1a]

Slight possibility of an EVAC problem, where even a bad gas cap can equal a vacuum leak. But even then, neither book is real clear on how it works or where things are located. The canister is under the spare tire, a check valve on the tank and an electric valves under the battery. Otherwise the books give a generic understanding of how it works and troubleshooting procedure.