After searching and reading through a dozen or more of the many threads that discuss rough idle, I haven't come across a situation that is the same as mine. So, I'm putting on my flame-proof suit and asking for some advice with my rough idle problem. If someone has found a thread that deals with the problem I'm about to describe, please point me to it!

The truck is a 1998, 5.4L with auto, and had about 83,000 miles on it. I've driven it since new.

The problem is very intermittent, although is beginning to happen more often now and occurs after being fully warmed up, driven for 15 minutes or more (doesn't matter if it is wet or dry out). When sitting in traffic, or at a red-light, in gear (drive) and sitting still for a minute or more, the idle will begin to deterioate (slow down and get rough). It doesn't happen all of the time, and only happens when sitting for at least a minute or more. At all other time (and before this happens), the idle is very smooth at about 600rpm or so. When this starts to happen, I can correct the problem (temporarily) by slipping it into neutral and blipping the throttle. Then, when I drop it back in drive, it is smooth again.

This problem started about a year ago. Since that time, I have replaced the plugs, and had the injectors professionally cleaned. After that, it still occurs, but isn't as rough. I conclude from this that the clean injectors and new plugs didn't solve the problem, but simply help the engine run a little smoother under the same problem condition.

I plan to clean the IAC valve and MAF sensor, but haven't done this yet. I would imagine that the TPS and O2 sensors may also be under suspicion. Maybe even something as simple as a vacuum leak?

Any ideas, solutions, things to look at, or other threads to read, will be most welcome. Thanks!

Alan

 

your year, engine and mileage scream IAC!

next time it is acting up (or down) tap the IAC with a screw driver handle and see if the idle changes.

while you are up against the firewall getting at the IAC you might as well replace the PCV hose because it is going next if it hasn't happened already.

your problem is very common.

good luck and welcome!

 

Hey, thanks!

I'll check both of those items out. I don't think I'll be able to try the "tap" thing, since it always seems to happen while I'm sitting at a traffic light somewhere.

I'll pick up a PCV hose and replace that this weekend.

As for the IAC - can it be cleaned, or should I just replace it??

Thanks again!

Alan

 

My 5.4 threw a code pointing to the IAC, so I replaced it. The Chilton repair manual states not to clean it, since damage to internal components may result. We are also having an erratic idle condition, and just got the engine light. Haven't had a chance to get it checked yet. I have noticed alot of gunk (read oily) in the throttle body and the old IAC that is guming up the works. I will try the PCV, check the code and see if that fixes the roughness.

Good luck with yours.

David

 

Hey hcmq-

Which PCV hose typically goes bad - is it one of the rubber ends, or is it the rigid plastic pipe?

Thanks,
Alan

 

It's the hose that goes from the PCV all the way back to the firewall and makes a hard right turn and then connects to the TB.

I believe it is a $25.00 part at the dealer and it includes a new PCV.

Yes I know the Chilton says the IAC is not servicable. However, they are talking about servicing the servo which is sealed. You can clean the ports which is usually the problem. Not a complete failure. What happens in 95% of IAC problems is the ports get gummed up and the plunger sticks. And yes sometimes it is so bad that they can't be cleaned enough so the whole thing needs to be replaced.

 

Thanks again. I will clean mine this weekend. I've read in other threads that carb cleaner and solvents like that are not to be used, while alchohol or WD-40 is the way to go. Do you have a preference on the cleaning agent/method for the IAC?

(and thanks for listening to my continuing questions )

 

What computer codes are present?
The IAC should not cause a rough idle but only change the idle speed. It only changes the ampunt of air bypassed around the throttle plate.
I would be looking at the EGR operation for sticking open. The exhaust gas coming back into the intake surely makes for rough idle.

 

Mine is a 98 exped. with 68K miles. Replace plugs,#4 coil,IAC, EVAP hose,fuel filter.Still runs rough,now CEL reads P0401(EGR).I hope this is the problem on my bad idle.

 

use "intake cleaner","brake klean", and wd-40.

bluegrass he said that is idle would get low and then get rough. he hasn't said that he has a rough idle.

most EGR problems present themselves as pinging "detonation". And if an EGR valve is stuck open the truck will barely run at all.

 

W2aew go to carparts on amwell road behind Shoprite ask for joe or chris those guys both know fords really well.

O yeah BTW im in Montgomery.

 

Cool - Thanks. I actually called them on Sunday to see if they had an IAC in stock (don't know who I talked to). He told me that they have them in the warehouse, and would have to order it (about $60). So, I decided to try cleaning it myself since I had already taken it off. I spent about 1/2 hour cleaning it with alcohol and WD-40, using flux brushes and q-tips and compressed air. I got the thing pretty clean. I also removed and cleaned the throttle body, as it was pretty gummy behind the butterfly.

This may have fixed the problem. I drove it around after I was done, and even let it sit idling in Drive for about 4 minutes, and it didn't get rough. But, it didn't always do it, so time will tell if I really fixed it or not. I took the "8" to work today... I'll have to drive the truck later this week to see if it still seems "fixed" or not.

Thanks for the tip on the local "Ford Guys" - that's always helpful.

Alan
(off 206 behind Mickey-D's / Cost Cutters)

 

Taking the advice of hcmq and others on the forum, I removed and cleaned the IAC. It was pretty gummed up, and it took about 30-45 minutes to clean using q-tips and flux brushes, alternating between isopropal alchohol and WD-40 as solvents, and compressed air to blow dry. I also removed and cleaned the throttle body (in spite of the sticker advising not to clean because of some "special coating" - what's up with that??).

I've driven the truck 3 or 4 times since then, and the problem has NOT re-occured. It's a little too early to say for sure that it is fixed because the problem was intermittent, but it sure feels like it is fixed!

Thanks again to the forum.