Bad MAS- Rough Idle?
Senior User
Joined: Jul 2004
Posts: 103
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From: Miami
IAC - thorougly cleaned, replaced cracked gasket between body and IAC, and no discernible crunchiness in plunger. If the IAC was bad, wouldn't it show a code?
Yes, did disconnect negative terminal for 22 minutes before reconnecting MAF terminal and taking readings.
Yes, did disconnect negative terminal for 22 minutes before reconnecting MAF terminal and taking readings.
Senior User
Joined: Jul 2004
Posts: 103
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From: Miami
On the PCV valve filter, assume this is inserted in-line, say 2"-4", before it meets the CAUTION FAN air hose (part 9B659 on my 93 4.0).
Went to my Ford dealer today, and they do not show as separate the rubber sleeve gaskets which fit over either end of this air hose. Any ideas where to find, other than a salvage yard?
Note that the IAC valve is about $65.
Went to my Ford dealer today, and they do not show as separate the rubber sleeve gaskets which fit over either end of this air hose. Any ideas where to find, other than a salvage yard?
Note that the IAC valve is about $65.
Senior User
Joined: Jul 2004
Posts: 103
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From: Miami
2nd PCV valve now in line, thanks!
Back to the IAC. As this is primarily an idling control, would a bad one have any impact on my dismal mpg? - currently at 12.8
I've read all the IAC threads and the test seems to be to disconnect the electric connection with the engine running. Change in RPM means its probably OK, no change = replace.
Back to the IAC. As this is primarily an idling control, would a bad one have any impact on my dismal mpg? - currently at 12.8
I've read all the IAC threads and the test seems to be to disconnect the electric connection with the engine running. Change in RPM means its probably OK, no change = replace.
Former ******
Joined: Nov 2004
Posts: 4,901
Likes: 2
From: Salt Lake City, Utah
It could, but my first thought, is that if the computer gives you a code for the MAF, there is an issue with the MAF. If you have cleaned it as described, and the code has cleared, then you got it. However, 12.8 is not very good economy for these. That suggests that something is very wrong. The MAF could do that, and the IAC could theoretically make it a little worse, but I don't think the IAC could make the economy that bad by itself. However, I would still try to clean it, and see if anything improves. Rough running at idle alone suggests IAC. Try letting it idle, and then raise to speed to just above idle, and see if it smooths out. Also, a vacuum leak coule easily make it run rough, and will also deceive the MAF.
On my '90 B2600i, I had a vacuum leak, and it was getting between 10-16 mpg. I found a vacuum leak, repaired it, and economy is now 19-26 mpg.
On my '90 B2600i, I had a vacuum leak, and it was getting between 10-16 mpg. I found a vacuum leak, repaired it, and economy is now 19-26 mpg.
Senior User
Joined: Jul 2004
Posts: 103
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From: Miami
MAF is new. IAC has been thoroughly cleaned. Starting when cold requires two starting attempts and idling is rough. Once above about 1500-1800 rpm, engine runs fine.
Will disconnect IAC when running and report back.
Will disconnect IAC when running and report back.
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Post Fiend
Joined: Apr 2005
Posts: 5,720
Likes: 5
From: Washington state
if you are still showing a MAF code with new MAF, suspect and inspect MAF connector, cable wiring, PCM/ECU and or it's connector or cable connector into it. Ford does make a breakout box for the ECU but it is expensive. Can open up ECU and measure and confirm correct MAF signal on the circuit board at connector. Each one of the sensor/accuator input/output circuits on the ECU has several components that can fail, surface mount devices, so not easily replaced. Do you have a ECU to sub in?
Last edited by 96_4wdr; Oct 6, 2005 at 12:04 AM.
Postmaster
Joined: Sep 2003
Posts: 4,452
Likes: 1
From: Southern California
Originally Posted by vintageant
No codes at all showing since new MAF installed.
Cleaning the IAC alone is not enough. You also need to clean the IAC passage. If you disconnect the air hose going to the throttle body, there is a rectangular opening on top of the throttle body inlet, just before the butterfly valve (for the 4.0L). That opening corresponds to a humped passage running back to the IAC. You need to spray into that opening with the engine running and the SPOUT disconnected (to keep the engine from quitting on you).
Senior User
Joined: Jul 2004
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From: Miami
Cleaned the IAC passage as described by Copper.
With engine warm and running, disconnected IAC electrical connection and engine noticeably dropped in rpm (~900 to ~ 700), but did not stop. Reconnected IAC connection and rpm shot up to about 1200 before dropping back down to 900.
Still "hunting' up to about 1800 rpm, then OK, and average mpg around town 12-13.
Pretty much about everything that has been suggested has been done, except replace the IAC
With engine warm and running, disconnected IAC electrical connection and engine noticeably dropped in rpm (~900 to ~ 700), but did not stop. Reconnected IAC connection and rpm shot up to about 1200 before dropping back down to 900.
Still "hunting' up to about 1800 rpm, then OK, and average mpg around town 12-13.
Pretty much about everything that has been suggested has been done, except replace the IAC
Elder User
Joined: Jul 2005
Posts: 560
Likes: 0
From: Houston,TX
when you say "hunting" do you mean a rise and fall of idle speed? if it is, this is what I was told meant cycling. replace the IAC. but remember, that bad mileage shouldn't be caused by the IAC alone. it basically just controls idle mixture.
when was your last emmisions test? if you don't have them, is the end of your tailpipe sooty black just outside the opening? this would be from a high hydrocarbon emission and indicates rich mixture. O2 sensor replacement and timing check.
hope this helps some.
Gary
when was your last emmisions test? if you don't have them, is the end of your tailpipe sooty black just outside the opening? this would be from a high hydrocarbon emission and indicates rich mixture. O2 sensor replacement and timing check.
hope this helps some.
Gary
Last edited by xuzme720; Oct 8, 2005 at 06:47 PM.
Senior User
Joined: Jul 2004
Posts: 103
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From: Miami
Gary,
Hunting is pretty much the same as cycling.
See: http://www.misterfixit.com/idle.htm
Florida no longer requires emissions test. Tailpipe seems OK. O2 sensor replaced 3-4 months ago.
As the engine did not splutter and die immediately when I disconnected the IAC as suggested by Copper, sounds like I need to replace.
Hunting is pretty much the same as cycling.
See: http://www.misterfixit.com/idle.htm
Florida no longer requires emissions test. Tailpipe seems OK. O2 sensor replaced 3-4 months ago.
As the engine did not splutter and die immediately when I disconnected the IAC as suggested by Copper, sounds like I need to replace.
Elder User
Joined: Jul 2005
Posts: 560
Likes: 0
From: Houston,TX
yeah, that's exactly what mine was doing, including not dying when IAC lead was pulled. I would go ahead and change it. worked great for mine. the other stuff was just some strange things mine was doing when it came time for emissions, just some ideas for better gas mileage.