Stumble, Surging and the infamous MAF, IAC, ect.

[fastcougar]

I have been plagued with this problem for about a month now and it just got worse after replacing the coil pack, plug wires and plugs (all OEM new parts).

Dead Link Removed

I don't think it got worse as much as it just got more noticable. Before yesterday, the problem only existed at a constant low to mid RPM run ... ala cruise control set or coasting. Now it misses so bad that it stumbles at idle to the point of nearly stalling. Before now, I have had a surging at idle since I can remember ... maybe the last 2-3 years. This combined with my "Howling" IAC in hot/humid weather, I think it's time to clean the IAC and/or replace it.

Last night I spent about 2 hours reading through search results and have come accross many writing about cleaning the MAF (Mass Air Flow Sensor - aka MAS) and IAC (Idle Air Control Valve - aka IACV).

These search results didn't include any pictoral how-to's and from the number of replies, I know that we are not alone. So, this weekend, I will be documenting everything very well when I do the following in an attempt to solve my surging/missing idle and constant RPM problem.

I will keep everyone updated on the results and links to the step-by-step how-to's with links to threads on this board describing the problem. Apparently, spending $267 (Fuel Filter[installing], PCV Valve [installing], 5 Oil Filters [I like to stock up], Coil Pack [installed], Spark Plug Wires [installed], Spark Plugs [installed], Idler Pulley [installed], Tensioner Pulley [installed], Acc Drive Belt [installed]) hasn't fixed the problem ... hopefully the next $15 will (security torx, O2 safe carb cleaner, wire brush).

Wish me luck! Also, if someone wants to do the leg work and gather up the links on these types of problem, please post them here.

 

[Jason_25]

Are your symptoms accompanied by a rough idle?

Also when you rev the motor in neutral does it seem to "miss" at certain rpm's?

If so, I bet that cleaning your MAF should do the trick.

 

[fastcougar]

I am very particular about how I do things. In order to pinpoint the problem, I would clean the IAC first (document as I go) and place it back on the truck. Start her up and see what happens. I prefer to do this as opposed to everything at once so that the true cause can be remidied. I am saving the MAF for last since it's the most expensive part Hopefully everything else will cure the problem.

Symptoms:

Idle: At idle, the car stumbles so bad that it almost dies. Then it will surge and catch itself, then stumble again.

Cruise: At a constant RPM, the car misses noticably to cause a stumble, like an injector is clogged.

I have yet to see what happens in Neutral reving situation.

Plan of Action:

1) Pull all the plugs and "read" them to determine if this is isolated to individual cylinders or across the board. If it's an injector, it should be isolated to 1 or more cylinders. If it's the MAF, it should be missing in all the cylinders.

2) Apply dielectric great to the plugs wire ends and clean the battery terminal and give it a good coating as well.

4) Clean Air Filter and reoil (I know not to over oil). Put back on and test. If test still shows problem, move on.

5) Replace Fuel Filter and PCV valve and test. If test still shows problem, move on.

6) Pull IACV and clean it. Put back on and test. If test still shows problem, move on.

7) Pull MAF and clean it. Put back on and test. If test still shows problem, repeat #6 & #7 and retest.

If problem persists, Most likely the injectors. I will be taking a 300 mile one way drive this weekend to run out the BG Products "44K" I put in. Once at my destination, I will add another can of 44K and drive home. If this doesn't work, I will have to conclude the problem is either the injectors or the fuel pump

 

[fastcougar]

Well, I was impatient to solve the problem, so, working right to left in the engine bay, I:

1) Pulled the IACV and cleaned it. Pluged it back in and started her up ... still stumbling badly at idle.

2) Pulled the MAF and cleaned it. Pluged it back in and decided to do things a little differently than planned. While intake was apart, I pulled the K&N and cleaned it.

3) While the K&N was drying, I pulled all the plugs and WHALAH ... #1 was completely smashed closed .000 gap Must have hit it against the header and/or threads installing it 2 days ago. Regapped it and reinstalled.

4) Applied Dielectric grease to all the plug boots and coil pack connectors as well as brushed the battery terminals and greased them as well.

5) Oiled the K&N and while waiting for it to dry, I installed the PCV Valve.

I started her up and she idled nice and smooth ... absolutely no surging or stumble. Must have been the #1 plug combined with the MAF. However, I still suspect the injectors for the constant RPM stumble since that is still occuring.

However, the constant RPM stumble is more faint. Hopefully the long milage fuel treatment this weekend will cure the problem. Tomorrow I will be changing the fuel filter. If the fuel treatment and filter don't cure the problem, my last two suspects are FPR and the Injectors. During the trip I will be monitoring the misfires to pinpoint the cylinders if indeed the injectors are to blame.

Anyone have any suggestion on other possible culprits?

 

[kps36]

You never mentioned it, but whilst you were doing all the work did you have your batt cable off and reset upon completion. I would go ahead and do this and see if all is well.

 

[fastcougar]

Battery was disconnected the entire time I was pulling the plugs and inspecting them as well as when I greased the battery terminals and the spark plug ends. In all, disconnected at least 30 minutes

I just want to know what else it could be. Other than FPR, Injectors and Fuel pump, the only thing I can think of is mechanical (sticking valve, worn valve seat, etc.).

 

[fastcougar]

The saga continues

The wife and I drove the Watkins Glen, NY this weekend (320 miles from Ashburn, VA). On the way there, I did some data logging with the AutoTap and found the misfires to be isolated primarily to cylinder #4 (65% of misses), followed by #5 (15% of misses) & #6 (10% of misses). The remaining misses where split dead evenly between #1, #2 and #3. Cylinder #4 was double checked for sparkplug gap and was at spec.

Once we got into town, I put the remaining bottle of 44K into the gas tank and filled her up. That evening, we drove around Lake Seneca (about a 80 mile drive). Today we came home, another 320 miles and it is still missing.

However, it's now only missing at a very predictable range. It seems to only be missing between 1200-1800 RPMs. That being the case, what are your thoughts?

I'm thinking it's the Fuel Pressure Regulator or #4 injector. However, how could the FPR cause a certain injector to miss? I'm guessing it's because the pressure would be highest near the regulator and pressure drop would be greatest farthest way from the FPR, which #4 is since the FPR is near #1. The fuel system layout looks like so:

#3 ------ #4

#2 ------ #5
FPR
#1 ------ #6


I will be changing the oil tomorrow after work and while it's draining, I will be repulling the #4 plug to read it and triple check the gap. Your thoughts???

 

[fastcougar]

I am planning on pulling all the plugs and regapping to .050 ... stock is .054 ... if this doesn't help, I can only assume that my initial suspesinions where correct. It's either the FPR or the Injectors.

 

[fastcougar]

Am I talking to myself or does anyone else have an opinion on this? This has to have happened to others on here!

 

[jwrezz]

Just found your thread, very interesting. I had been having similar problems since I put in the Bosch P+4's. My miss fire's were limited to #3 (I had posted about this too). I had a miss in #5, but only once and the plug was fine. #3 I replaced the plug (bosch) 2 times both times looked like it was burnt up. ONe time it was smashed shut (all 4 electrodes) like it was banged up on installation. I went back to stock autolite platinums, and OEM wires and haven't had a miss yet (about 1000 miles), but still feels odd for about 10 secs on a cold start. I'm gonna pull that plug again when I hit 1000 exactly and check it. I'm thinking an injector still may be bad, but, and this is a big BUT, w/ that one plug that was smashed up, I was fearing the worst, and I still have the thought in the back of my mind that I may have a problem in the valve train some where. Now that would suck.

I also have that NASTY moan/whistle on hot humid days. I pulled the IAC off. Chilton says use a new gasket, but mine didn't even have a gasket on it (could that be the problem?), it looked like 2 o-rings on the manifold. I cleaned it (IAC), and where it meets the manifold w/ gumout, also cleaned the throttle body w/ it (says it's safe for it). Still heard a little whistle today for a few minutes after sitting out in the sun in a parking lot, but it was a bit cooler here today (low 70's) and it went away quickly. But when I put my ear next to the truck to try and pin point it (like on those really hot humid days when it's REALLY loud), it seems to be coming from the front pass. side corner (where the filter is). I've pulled the filter off, and it remains. I put my ear next to the end of the intake tube (filter off) and it sounds like its coming from inside it some where. That IAC thing really makes sense, but I dunno! Any way, I'll keep you posted as I progress ( I still have a rebuilt half shaft to put in too!!), and I'll check back here for your progress. Best of luck!

 

[fastcougar]

Change the oil today since the trip put me over the change interval. While the oil was draining, I removed spark plug #4 and measure it ... sure enough, the gap was 0.057, 0.003 over, so I regapped to 0.050, 0.04 under (better under than over). After the change was complete, I test drove to see if I could get it to stumble again. I couldn't get it to stumble, so it turned out to be as simple as spark gap!!!

This weekend I will be pulling the others and regapping to 0.050 to ensure that this will not happen again. I had no idea that spark gap varience of so little could have such a drastic effect. So, if you are stumbling, check spark plug gap first with an acurate gapper.

 

[Jason_25]

So what are your knuckles looking like right now?

For sure you scraped them up a bit changing plugs so much.

Congrats on isolating the problem.

 

[fastcougar]

Actually, to my surprise, no blood has been sacraficed to the car gods in the hunt for this problem's cause However, my fingers are very sore and I have have a bald spot from scratching my head so damn much! I have however learned one very valueable lession ... stick to the basics first and always trouble shoot the problem from the cheapest standpoint first. This Saturday I will be pulling all 6 plugs, regapping to 0.050 and reinstalling. Also, my pictures of the original MAF cleaning didn't turn out so hot, so I will be reshooting that as I clean the MAF one last time for good measure

Oh, that reminds me, the Howling problem wasn't solved ... the car howled like a wolf under a full moon on the way to Watkins Glen when we stopped for food. Outside temp ... 85 degrees with slight humidity (probably around 20-40% ... not sure, but not sticky). I mention this because when I was cleaning my IACV, I noticed that it appears that the plunger that opens/closes between the two chambers is operated different than I thought. The solenoid forces the plunger shut (pushes it up) an overhead spring forces the plunger open. I noticed that when the plunger was fully closed, it was still slightly open. Is this normal? My thoughts on the matter:

Throttle plate is closed, TPS tells the ECU "open the IACV or the engine will die" and the ECU send a signal to the IACV. I think that the power is cut to the solenoid and the spring pushes the plunger down, allowing air to flow between the chambers and thus into the engine. When under throttle, the ECU knows this by TPS readings and thus applies power to the solenoid and the plunger pushes against the spring to close. Is this how it works or is my logic backwards?

 

[jwrezz]

That makes sense to me. I noticed that mine was open just a bit when I cleaned it. Do you know what the little black plastic "thingy" is that sticks out of the side? I thought it may be an adjuster, but it just seems to spin loosely, like it's a cap of some sort. thanx again.I'm gonna pull all my plugs this wknd and gap to .050!

Oh, btw I've got that down to a science too. Pass side back 2 thru the fender (w/ a u-joint on the socket). All others from the top. I can do all 6 in less than 1/2 hr. The TT allows easy acces to those back pass side. I'd hate to do it on a lowered one!

 

[fastcougar]

Originally posted by jwrezz
That makes sense to me. I noticed that mine was open just a bit when I cleaned it. Do you know what the little black plastic "thingy" is that sticks out of the side? I thought it may be an adjuster, but it just seems to spin loosely, like it's a cap of some sort. thanx again.I'm gonna pull all my plugs this wknd and gap to .050!

Oh, btw I've got that down to a science too. Pass side back 2 thru the fender (w/ a u-joint on the socket). All others from the top. I can do all 6 in less than 1/2 hr. The TT allows easy acces to those back pass side. I'd hate to do it on a lowered one!

Exactly the way I do it I will document this with a pictoral how to when I complete my research and post on how to clean the MAF and IACV.

 

[Lifted95X]

I just cleaned my IAC and let me tell you its very temporary. You can take it out clean the passages, pop off that little black button looking thing and their are two filters under there. I cleaned everything with throttle body intake cleaner and the sound was gone......for about 2 days. But at least it will show you that it is the part that is making that horrible HUMMMMMM.

 

[morphous]

all,

I have found changing spark plugs is made much simpler by using some stiff 3/8 hose. You put the plug in hose and you can flex it into any position. Works like a champ for me all the time. However, do what works best for you.

Fastcouger, I am looking forward to your pictorials on MAF cleaning. I have an uneven idle which I believe to be MAF related.

Later,
Morph

 

[jwrezz]

Are we talking about the same black button? It pops off? There's a black plasting thing on the back of the unit where the wiring plugs in, and then a black plastic cylinder maybe 3/4" in diameter, and 1" deep. It has a thin stem on the back side that goes into the side of the valve. Mine spins and I was thinking it was some kinda adjustment. I don't notice any movement of the valve itself when I spin it though. I don't wanna pop it off, for fear that it's not supposed to come off. Thanx for any help,

 

[jwrezz]

OK, I did pop off the little black button. But I can tell that it's 2 pieces. I pulled both off the vavle housing and there was a little intake tube that goes back into the vavle. It looks like a little vacuum port. I guess that the 2 little filters are inside the plastic button? And air is sucked in thru that plastic piece, thru those filters and into the the IAC itself? What for? Well, all I know is that I pulled the whole thing off, even the little black thingy, and cleaned it all w/ gum out (again) thoroughly. I think the valve is open when it's not getting power, and closed when it gets power? Vavle was open after I disconnected it. So the spring pushes it open, and the electrical plunger closes it, I'm assuming. Well, I'm letting the whole thing dry out in the sun. It's a nice hot and humid day here in NJ, and the thing was howling like a mad man. May be this'll fix it up. I'm gonna put it back on in a bit and take a ride. Hopefully it'll still be hot and humid so I can test it. Just gotta get outta here before the rain comes in and cools things off! Here goes! I'll get some pics in for the next post...

 

[fastcougar]

I often wondered what that little black nob was for ... twisting it does absolutely nothing! As for these "filters" that you are talking about ... where are they? Diagram them in your post. BTW, what year/engine is in your X?