Idle Surge

[jwarwick]

I have a 2003 Explorer with the 4.6 and 135k. About 3 months ago, while the Ex was traveling between 45-55mph, it would feel like the trans was slipping in and out of gear. I had my mechanic look at it and he replaced a coil pack and spark plugs and this fixed that issue.

A week later, while coming to stop in a parking lot, the Ex stalled on me. I put her in park and she started right back up. She would continue to stall while decelerating. I cleaned the IAC but the stalling continued, so I replaced the IAC valve and TPS, and cleaned the MAF and throttle body. This fixed the stalling issue.

Everything was great for a month or so, then the Ex started “idle surging” when I would come to a stop. When I would hit the brakes, the idle stays up, and the Ex fights you (wants to accelerate) until you get to about 5mph, and then the idle will suddenly drop to normal, and you come to an abrupt stop because you had to push the brakes so hard to fight the engine.

No codes have been thrown since this started either.

I cleaned the PVC lines and the two rubber elbows that go into the intake manifold. Neither the lines nor the elbows looked worn or bad. I have checked for vacuum leaks with carb spray and didn’t find any.

With the IAC disconnected, the Ex will idle like normal until you apply pressure to the brake, then the RPMs will lower to 500 and it tries to stall.

Could I have a bought a bad IAC valve??

Could it be something with the MAF or EGR valve?

Also, ever since I replaced the IAC, when I start a cold engine, the idle jumps up to about 1500 RPMs for 30-40 seconds, then it jumps up to about 1800 RPMs and then drops immediately down to a normal idle (700-800). i'm not sure if this is a related issue or not.

Any help would be appreciated! thanks

 

[Number4]

As it occurs when you press the brakes, I'd suggest looking at the brake booster.
It relies on engine vacuum.
Could be the line, could be the port the line connects to, could be the booster itself.

 

[jwarwick]

thanks for the info! I didn't have time to check the brake booster yesterday, but I should be able to today.

!!Strange Update!!

As of this morning, when i started a cold engine, it idled at 1100 for 20 seconds and then dropped down to 800. After 10 seconds at 800, the idle started jumping up to 1400 and back down to 800. It would continue to jump up and down for a couple minutes. i turned the engine off and back on and the idle jumping continued. I put the Ex in reverse and the idle jumping continued, making the Ex move without pushing in the gas pedal. It also continued in drive. The idle jumping continued at low speeds for another 5 minutes. After that, the Ex drove fine and idled like normal. I could not get the idle to jump again after driving the Ex for 20 mins.

 

[jwarwick]

The Ex has not had an idle surge while braking in a couple days. But the idle is still jumping at a cold start, which is new.

I cleaned the vacuum line and sprayed around the booster checking for leaks. I couldn't find anything.

Is there anything else i can test with the brake booster??

 

[SyberTiger]

Did you ever find the solution to your problem?

 

[lincolnshibuya]

what kind of IAC did you replace it with? only Motorcraft works.

my wife complained about this stalling issue but I can't replicate it, then 1 day after I replaced my rack and pinion and did a test drive, I noticed that coasting downhill (and not putting in gas) the throttle would go up and down which I found so strange. So I cleaned up my IAC and after that it's even worst, it even wont start without pressing the gas pedal at idle or startup, it stalled everytime.. I just told myself I shouldn't have cleaned it (it was at least better before) It was probably cleaned 2x in its lifetime and probably on its last leg. Ordered a new motorcraft unit from Amazon ($97) since the dealer price is outrageous at $185! and it just started right up and idles at the right rpm.

 

[SyberTiger]

FYI...you can read THIS POST concerning erratic idle including when you aren't pressing the fuel throttle.

 

[jwarwick]

**FIXED** well sort of...

so it has been roughly 6 months since i've experienced the idle surging. here is what i did to "fix" the issue:

After the new Motorcraft IAC didn't fix the issue, I was thinking I got a bad part. so I did some reading and found the 'idle set screw' in the IAC (I don't believe all IAC's have them). So i played with this set screw a bit, changing the idel RPMs. Well, my Ex would idle around 700 when it had it's problems. so i eventually set it to idle at 800-850 and like magic, i haven't had the **knock on wood** idle surging issue.

I also removed and cleaned all the hoses and tubing with carb cleaner and made sure there were no leaks as well.

I'm sure it isn't recommended to mess with the idle set screw, but it has worked for me so far. However, I have noticed slightly worse gas millage (maybe a MPG or two less than normal) but i'll take it!

 

[Number4]

Your MPG went down because your using more gas at idle. The 4.6 is set to idle at 600 rpms.

While you may have found a solution for the symptom, I'd be concerned that you're only masking an issue that may become worse, if not catastrophic.

Might consider taking it to a shop.

Reading (skimming) your original post, I don't see that you've cleaned the throttle body. The valve may be gummed up in a fashion that causes it to stick, then break loose only to return to the sticking point. Over coming the sticky point may result in a sudden increase in air flow.

Try these, do the reset last though.

PCM reset:

http://www.explorerforum.com/forums/showthread.php?t=396533

Throttle body clean:

https://m.youtube.com/watch?v=JPNnHU6PYbo

 

[jwarwick]

I cleaned the throttle body a couple times, I just forgot to mention it.

I've had it to two shops and neither could find the problem. One of the shops had the vehicle for 2 days and put 30 miles on the Ex and never experienced the issue (this was before I made the changed the idle). The issue didn't happen every day, but it would happen enough to make you worry about stopping/braking.

I'll check out the resetting the PCM when I have time.

thanks for the input!

 

[lincolnshibuya]

**FIXED** well sort of...

so it has been roughly 6 months since i've experienced the idle surging. here is what i did to "fix" the issue:

After the new Motorcraft IAC didn't fix the issue, I was thinking I got a bad part. so I did some reading and found the 'idle set screw' in the IAC (I don't believe all IAC's have them). So i played with this set screw a bit, changing the idel RPMs. Well, my Ex would idle around 700 when it had it's problems. so i eventually set it to idle at 800-850 and like magic, i haven't had the **knock on wood** idle surging issue.

I also removed and cleaned all the hoses and tubing with carb cleaner and made sure there were no leaks as well.

I'm sure it isn't recommended to mess with the idle set screw, but it has worked for me so far. However, I have noticed slightly worse gas millage (maybe a MPG or two less than normal) but i'll take it!

I don't think the Motorcraft IAC has an idle screw adjustment. I just recently replaced mine and got the old part. You sure you have the motorcraft IAC or the "OEM" (not motorcraft) brand?

 

[jwarwick]

UPDATE

The IAC I replaced first was not a Motorcraft part. I have since replaced the IAC with a Motorcraft one. The idle seems to be a bit better, it is not as rough now, but my RPMs are still very high (between 800-1000) at a cold or warm start. I have cleaned the EGR valve port as Syber showed in another post.

I reset the PCM as request by Number4. I'm not totally sure this did much.

All this was done two weeks ago.

My problem now is that the shift points seem to be way off. Because the idle is still high, it seems like it is shifting later.

If I go slow on acceleration and keep the RPMs close to 2000, then it seems to shift fine. But I drive like normal, the shift patterns seem way off.

For example, I have been in the high 60s mph before it shifted into 5th. This has happened quite regularly.

Any thoughts??

I appreciate all the help so far.