Sudden rough idle

[Guido0136]

Hello all: I have had this problem for about 2 weeks now and have read through many threads and still have no idea about this.

1994 ATX with 207K

About two weeks ago while idling while engine hot the engine started to 'bog' down a bit a felt almost like it wanted to stall. While over 1000 rpm it runs fine but as soon as you take your foot off the pedal it starts to stutter.

If you start it cold, it runs just fine but after 1-2 minutes when it gets warmed up, it started to stutter. I have removed the MAF connection while idling and there is a slight increase in RPM's but the stutter remains.

I don't see or hear any vacuum leaks and I have also taken (bad cell phone) video. Can you guys help me narrow down what the next thing to check is?

Thanks,

http://s258.photobucket.com/albums/...ction=view&current=VID00011-20100725-1014.mp4

 

[rubydist]

the first thing to do is check for codes - any?

I can't really hear what is going on in the video on my computer, but rough idle is commonly caused by bad iac not controlling idle speed correctly or dirty mafs not measuring intake air quantity correctly. I would be tempted to clean both of those anyway, if you haven't done so recently.

 

[xshoel93x]

i had same sort of problem, it would idle rough and nearly stall out or even stall out sometimes, warm or cold. took the plug off the airbox and bent the pins a lil bit for a better connection and it seemed to work (it was already cleaned) temporarily. does it every now and again but w/e

 

[Guido0136]

Okay I have heard of the IAC and know what it does. but where is it? I will also check the airbox sensor to see if that it getting a clean connection.

Thanks,

 

[luigisho]

The IAC is the cylinder/sensor on the intake above the throttle body. It can get gummed up. There is a reusable gasket so keep an eye out when you remove it. Clean the MAF filament with electronics spray cleaner.

 

[Guido0136]

I have two MAF's and both have been cleaned. No difference between either of them. So my next thing is the IAC. Do you have a pic of this?
sorry but I'm no professional mechanic.

 

[jmpSHO2nd]

It's in the pic or vid that you posted. It is slightly to the left of the throttle body and on top of the intake and it's held on by two allen bolts, the bottom can be a little of a pain too get to.

 

[jmpSHO2nd]

Also I never had any luck cleaning an IAC so just because you clean it and reinstall it does not mean you fixed it if that is your problem.

 

[luigisho]

It looks like this. http://www.bestvalueautoparts.com/item.wws?sku=28943&itempk=678839&mfr=BWD AUTOMOTIVE&weight=1

One of the allen bolts is harder to reach and you need a long extention. Don't drop the small bolt or the gasket.

 

[Guido0136]

Gotcha - I know where that is from the black plastic 'hat' I'll see if I can get this off tonight.

Thanks,

 

[luigisho]

http://www.shotimes.com/php-bin/mod...le=article&mode=thread&order=0&thold=0&sid=82

I forget but I thought there was a model year change where it can't be cleaned effectively any longer.

 

[Guido0136]

Okay so I managed to get the IAC off. This is my first one to pull off so I'm not sure what a clean or dirty one looks like. I cleaned it out with CARB cleaner and some dirt came off, but not a lot. After it dried, the ring on the shaft was able to move freely against the spring. It did not feel like it was being hampered.

Installed the IAC back on and started her up. As usual, during the first 1-2 minutes it ran fine, then after two minutes I can hear is trying to stumble. After 5 minutes it is running but anything under 1000 rpm's it sounds like it's missing. How do i know if the IAC is bad? I do not want to throw money at it. When I pulled the IAC harness the car stalled right away. Plug it back in and she started right up.

Over 1000 RMP's it runs smooth and strong.

Any ideas?

Thanks,

G.

 

[CWhalenSHO]

I had the same problem. I would replace the IAC. I completely disassembled my intake and cleaned everything with Berryman's B-12 cleaner including the IAC.

I replaced my IAC and the idle issue went away. The bottom bolt was a pain to remove. I actually removed the entire intake to get to it. (I think I can now remove the intake in about 25 to 30 minutes) Once I swapped it out, no idle issues.

I know you don't want to just throw parts at the car but you can pick up a new IAC for like $60 at Advance. You can also try to swap it out with a known good one.

What is maintenance history on the car?

 

[jmpSHO2nd]

I agree with replacing the IAC but I would also try to clean the MAF first.

 

[Guido0136]

MAF is clean - I have two of them and both are clean and both do not change the issue. I'm up hear in Canada, so I'll poke around to see what a new IAC costs.

Thanks guys!

 

[Guido0136]

So IAC's here in Canada go for about $100 and change. Still not sure it's the IAC. I'll have to run codes to be sure.

 

[jmpSHO2nd]

So IAC's here in Canada go for about $100 and change. Still not sure it's the IAC. I'll have to run codes to be sure.

Alot of times you won't get a code for a bad IAC and if you do decide to replace it do not get one from AZ. I replaced mine on my truck from AZ and 2 in a row right out of the box were no good and the one that is in there now is acting up and it's only about a year old.

 

[hawkeye18]

If it only happens at idle, and not with throttle applied, then the component at fault must be one that is in use during idle and not when not in idle. This leaves only the IAC as the possible fault source. There is a very slight chance the DIS might be failing, but it's like, 4%.

ATX IACs cannot be cleaned, and in any case, if the electronic section of the IAC (the tube with the plug on it) is damaged or malfunctioning, obviously cleaning isn't going to work.

Go to rockauto.com and get an IAC there. I see a Kemparts IAC on clearance for $35US ($36.27 canadian [really? that low?]), and shipping to Canada shouldn't be more than ~$10-15.

 

[Guido0136]

Cool, I'll check it out!

 

[Guido0136]

Great timing! Ordered it for about $60.00 Canadian, thanks so much, I'll keep you guys posted if it solves the issue.

Thanks again.