Help! Rough Idle

[ddenton749]

1993 Explorer, V6, 177,000 miles, automatic.

The problem: This started about two days ago. The idle is generally rough. If it sits idling (like in traffic) it will stall if I don't tap the gas. If it does stall, it starts right back up again. It runs VERY rough when the engine is cold. It behaves like it has a vacuum leak but I can't find one. The vacuum gage reads 14-15 inHg. Compression is good. Plugs are good. I replaced the upper and lower intake gaskets last October (water leak) and it has run fine since. I re-torqued the intake bolts but they seemed tight. I replaced the water pump on Sunday but I doubt that has anything to do with it. I also cleaned the Air By-Pass Valve with carb cleaner.

Could it be a bad Air By-Pass? Bad or dirty MAF?

Probably Unrelated: I'm not getting current to the fuel pump relay to activate the fuel pump. The car runs fine if I jumper the fuel pump relay terminals. Is it a bad EEC? Could this be related? The inertia switch is good.

Anyone can respond to ddenton@kellyengineers.com as well as to this thread.

Thanks,
Don

 

[DonM]

Maf or IAC could cause those problems. How are your Plugs and wires?

BTW, how did you check your Vacuum Pressure? Where did you run the gage?

Im still having a slight engine roughness and would like to check for vacuum leaks.

 

[ddenton749]

Re

Hi Don,

Thanks for responding. I attached my vacuum gage to the same vacuum tree as the brake booster, etc. The reading was 14 to 15 inHg. That's a little bit lower than I would expect. (16 to 20 inHg)

Plugs and wires are probably about a year old, give or take. I had the plugs out yesterday (Bosch Platinum) and they looked good. While they were out, I did a compression test - all around 150 psig.

A slight engine roughness I could live with. It's the stalling that's making me crazy. There may be a ever-so-slight decrease in overall performance, but I notice it because I've been driving the X for five years.

The IAC (idle air control) valve is the same as an ABV (air by-pass valve) right? It's mounted on the driver's side of the air plenum and has one electrical plug? I've had some issues with that in the past. I've had that off before to clean it when I had some cold-start problems.

I read somewhere that a clogged catalytic converter could be the culprit. What do you think?

 

[DonM]

Bad Cat could cause that!

Awhile back I had problems when coming to a stop, either a red light or stop sign. The truck felt like it wanted to stall almost every time. Never did though. Bad 02 sensors fixed this problem.

Maybe your 02 are shot causing your engine to stall?

The vacuum pressure sounds a bit low. Im told a slight leak could cause the engine to run rough!

Did you buy a vacuum guage or did you make one?

 

[ddenton749]

Re

Hey Don,

A partially clogged Cat. Conv. would cause low vacuum readings. The vacuum gage is a Snap-On Tools gage. I've had it for years. I used to be a mechanic in a time when cars were much simpler.

I have a cheap EEC code reader. It's never given me any indication that I have a bad O2 sensor or lean/rich codes. In fact, the only codes I have gotten are for the fuel pump circuit - 543 and 556. I believe these codes and the rough idle are two unrelated problems.

How long do Cat Converters last? This one is original with 177,000 miles.

Don

 

[DonM]

Don, when my 02 sensors were bad, i never had a check engine light come on. I scanned for codes and none were found! You can check the 02 sensors(do a search on them)

As for the Clogged Cat, Im not sure of there age? But you have 177k miles, it might be a good idea to have them looked at.

 

[ddenton749]

Yeah, I know, I'm responding to my own thread.

I've talked to a mechanic friend. He pointed me to the throttle body. He said it's a common problem with Fords that the throttle gets very dirty and causes the symptoms I mentioned. Another common problem is the IAC valve. He described them as "Notorious". He also said that while Cat Converters can go bad, it's very rare.

He offered to put it on his Snap-On scanner (not for free I'm sure) to pin-point/eliminate O2 sensors, etc.

I'll let you know.

 

[DonM]

Yeah, let me know how ya make out!

BTW, being as you have 177k. The 02 sensors should be changed anyway. Atleast that's what alot of members here claim.

Like i said, the 02 sensors was apart of my problem and it sounds like that's is your problem also.

 

[ddenton749]

Update

I solved the fuel pump power problem (see thread-name search ddenton749) and was able to continue with the code scan. The KOER test gave the codes 136 and 172. Both of these describe a lean condition in the O2 sensors bank in 1 and bank 2. The book said something about the voltage not changing? Is this indicative of bad sensors or does this point to a different problem like a vacuum leak? Any and all help is appreciated. Thanks.

 

[DonM]

Don, your 02 sensors are bad! If they are not switching back and fourth or they switch slow, they are bad!

You can test them using a Voltmeter, i believe? If you dig deeper useing the search feature, you will find the exact #'s the 02 sensors should be running at! I cant remember the #'s.

 

[ddenton749]

Re

Thanks, Don. I have a manual that describes the proceedure for checking O2 sensor voltage. I sounds like a bit of a PIA and I need a digital meter, not an analog type. (Analogs draw to much current to swing the needle-we're measuring 0.1 - 0.9 volts) Are there only two O2 sensors? Is it likely that MORE THAN ONE has gone bad at the same time? Maybe there's a vacuum leak I haven't found yet? You seem pretty sure that if they're stuck in the lean voltage range they're bad.

I might try to borrow a digital multi-meter and run the test before I go through the trouble and expense of replacing the sensors. I guess it depends on how much they are.

I'll keep you posted.

Don

 

[dogfriend]

Originally posted by ddenton749
Another common problem is the IAC valve. He described them as "Notorious".

I would describe them as "infamous". Your stalling problem could be a sticking IAC valve, especially if you also get an abnormally low (<500 rpm) idle speed.

This thread reminds me of the Monty Python skit where everyone is named "Bruce"

 

[ddenton749]

IACV

Hi Dogfriend,

I took the IACV off, took it apart, cleaned it with carb cleaner and blew it out with compressed air. The problem still persists. Could the infamous/notorious IACV still have some kind of internal problem?


Rule number 1, NO POOFTAS!
Rule Number 2, I DON'T WANT TO CATCH ANYONE NOT DRINKING!
Rule Number 3, NO POOFTAS!......

Thanks, the saga continues...

 

[dogfriend]

When mine failed, I could see where the shaft was rubbing on the housing,causing it to stick closed. This only happened after the engine was warm and when I tried to restart after driving a few miles.

I dont want to catch anyone NOT drinking

 

[ddenton749]

IACV

dogfriend,

I just talked to the local Ford dealer and an IACV is $116. I'm going to make doubly sure that's what it is before I throw one at the problem. Here's a question for you: Do you remember how stiff the valve return spring is. When I had mine apart, it seemed very easy to push the valve open.

I'm also going to try to verify the O2 sensors. The codes (136, 172) are telling me they are reading a lean condition. Which would make sense if the IACV was open too far.

Oh, Emmanual Kant was a real piss-ant who was very rarely stable....


Thanks, I'll keep you posted.

 

[Runnin'OnEmpty]

Dondenton, earlier in this thread, cleaning the throttle body was mentioned. Have you cleaned it? If not, try cleaning it, especially where the throttle plate closes against the housing. Carbon tends to build up there, and restricts the airflow at idle.

I have to do this every couple years on my Cherokee, and the idle symptoms are identical to yours.

 

[DonM]

A bad Iac could cause the problems your having, but I still say your 02 sensors are shot.

When mine were going bad, it would cause the engine to want to stall, but never did. I measured the 02 sensors and they were switching slow. Yours might be completely shot, causing your engine to stall all the way!

 

[dogfriend]

Re: IACV

Originally posted by ddenton749
dogfriend,

I just talked to the local Ford dealer and an IACV is $116. I'm going to make doubly sure that's what it is before I throw one at the problem. Here's a question for you: Do you remember how stiff the valve return spring is. When I had mine apart, it seemed very easy to push the valve open.

No, sorry, I dont remember how strong the return spring is. The thing works by opening and closing proportionally to a pulse-width modulated signal sent by the computer. I dont think that the spring has to be very strong to close it off, but I am guessing here.

$116 is too much for the IAC. I only paid $60 from the dealer two yrs ago. Try www.fordpartsnetwork.com or aftermarket like Napa or Autozone for a better price.

I'm not convinced that your IAC is bad, but the problem with it stalling at idle was similar to the problem I had with mine, but there are other components that can cause the problem. When it is about to stall, if you crack the throttle a little bit, does it idle okay? If so, then I would bet IAC. If not, something else.


Socrates himself was permanently pissed

 

[DonM]

Im not sure how true this is? But i was told if the IAC is bad and causes the engine to stall, more then likely you will see black smoke coming form the exuast?

A tech told me this a few years ago.

Im not so sure about it though...

 

[dogfriend]

This didn't happen when I had the problem with my IAC. I never saw any black smoke. The truck ran fine other than with the engine warm at idle. No CEL either, because there is no feedback to the computer from the IAC.