Hey Guys,

I've got an 04 Ranger with a V6 4.0 SOHC, about 303k miles, and recently while stopped at a red light I'll notice a slight drop in my RPMs and stutter. Usually I'll idle around 750 and it will drop like 10 or 25 (or 50, can't really tell because the scale). It will immediately go back to where it was and be okay again. It can happen a few times in a row or once during a stop. It will also sometimes happen while coasting at low speeds. I haven't noticed any issues while driving or accelerating though.

From reading the forums I saw people mention cleaning the MAF and IAC so I tried cleaning them. The MAF wires looked clean but I still lightly sprayed them and the IAC on the other hand was really dirty so I cleaned it good. This didn't seem to help though. Also, last week I put a can of seafoam in the tank before filling up hopefully that would help. I'm almost ready to fill up again, drove about 250 miles so far, but it is still doing it. The air filter is new and I just replaced my fuel filter this weekend. The spark plugs and wires are less than a year old so I doubt it is those.

Do you guys have any other thoughts of what it could be? I'm worried it could be a bigger issue so I don't want to just let it go. I took it recently to get an oil change and they didn't notice any issues. So I'd have to pay for a diagnostic test to have them look into the issue further.

Any help would be greatly appreciated, if you need anymore information, please let me know.

 

Is this just as you stop? or after you've been stopped a short while?

Is this an auto or a manual?


Mine is doing this too, but it's dropping far enough to cause the oil pressure gauge to flick off, i cannot find a cause yet.

 

Sometimes while stopping or right after
stopping then other times after sitting there for a little bit. It seems very random, I've tried turning off my AC thinking that might be related but it doesn't seem to change the frequency.

Automatic. I do have a few oil leaks but nothing major, my oil level doesn't get low between my oil changes (I get one every three months). I've had no lights come on at any point.

 

Hmm, auto makes this quite different, drop it to neutral as you're about to stop, does that prevent this problem for you?

 

I haven't tried that while driving but the drop does happen while in drive, neutral, and park (haven't tried reverse). It doesn't seem to start right after starting my truck but will happen after stopping once or twice.

 

Ohhh, ok, that's different from what i was thinking then.

Alright, so you basically have an idle issue, but possibly related to your brake booster.

If your engine is up to running temp and the vehicle has been turned off - if you then start it up and leave it in park, don't touch anything, don't start the vehicle with your foot on the brake (no idea why people do that) let it sit, will it have the idle problem in a 5 minute period?

If not, go ahead while it's running and push the brake pedal (still in park) give it a firm push. Does the idle have issues then?

 

I think it could be the brake booster then, I've noticed it happens less if my brake is fully down. As I slowly release it (but don't start moving yet) I'll notice it happen more. I'll try those tests when I go to leave work and let you know what happens.

I did a little research on how to replace it and saw people mentioned bleeding the brake lines. I don't know how I feel about doing that myself so I might have to take it to the dealer to get it fixed. I want to make sure that is the issue before, would these be the best tests to make sure it is that. I've never noticed any braking issues, my stopping power and response seem to be great. I'll double check the lines that go to my brake booster too while doing those tests.

 

If it's only bleeding brakes you're worried about, that's really easy even on your own (just place container above height of bleed nipple). But no problem having a shop look if you need.

If there is a leak in the booster system, my thought is that after a stop, it's taking more to replenish the boost level, causing the engine to dip for a moment, but i can't really go much further than that i'm afraid.

 

So after driving home I sat in neutral with my tires against a stop. I didn't have one drop same for when engaging the brake. While in drive in the same position I had one or two very small drops. Once engaging the brake I had a few more drops, seemed to be at the same rate and size as just in drive. These drops were smaller than what I usually get out on the road at a red light. While in park I didn't have any drops. With my brake engaged I had no drops. I coasted around going around 10mph and 20mph with no drops. When braking hard I noticed the RPMs would increase then drop back to their previous level. Note, I had the emergency brake on during these tests, not the coasting ones though.

Does any of that help you?

 

Here is a video of a drop: https://www.dropbox.com/s/6io1m3347cpom58/Drop.mp4?dl=0
It happened while leaving my work, I was stopped in drive with the brake fully engaged.

 

Um, is that it?

Does the engine actually drop too? or is it just the tach needle?

 

Both, I feel a shutter when it happens, the whole truck seems to shake. I know it doesn't seem to be a lot but it just started doing this. I've never had any issues like this in the seven years I've owned her. Plus, with the mileage I'm worried it could be the start of something bigger.

 

Hmm, not likely - however, you should run a strong dose of injector cleaner through it, something like Redline S1 something or Chevron concentrated (only the concentrated, not the other versions)

 

I can pick up some Chevron Concentrate after work and give that a shot (AutoZone doesn't have Redline). Do you usually change your oil after using the Chevron? I just got an oil change Friday, but I don't want to wait three months to give this a shot. I just used Seafoam before my oil change when I started noticing this issue, by the way.

 

No, and if you're heading to Autozone, they do the large 32oz bottle, cheaper to buy more, you'll always use this stuff.

And no, no oil change needed, it's a PEA based cleaner and just run it in your fuel - i think i put 24oz in my last tank.

 

Sweet. So if this doesn't work should I just leave it alone and stop worrying about it so much?

 

Unless it progresses to anything else, i wouldn't worry about that at all, for now at least.