• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

1999 Mazda/Ford intermittent near stall and stall at red lights and after coming to stop...


1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
The stalling or wanting to stall issue is intermittent. It only happens when coming to a stop (while winding down to idle.) It will mostly almost stall, but picks back up at the last second before stalling and if I have a load (like A/C or while turning) it will stall. It always restarts without issue. FYI: Battery change (which was due) had no effect and the near stall and stall occurs still with new batt. FYI: MAF cleaned and PCV cleaned.
The engine seems to hunt around for the a stable idle at times and vaguely wavers and does not set hard at one particular RPM. I have no engine light warning and the issue was occurring very intermittently before the catalytic converter and oxygen sensor replacement and still occurring after that. I suspect I need to clean the throttle body, but is there anybody else who runs across this?
Thanks in advance and thanks for being here.
 
Last edited:


RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Engine computer uses the IAC(idle air control) Valve to set idle RPMs based on engine coolant temp

On cold start does the computer set idle at 1,100rpms, and then slowly lower idle RPMs to about 750 over the next 5minutes(warm up)
This means ECT sensor is working and computer is successfully controlling IAC Valve

Also any time you start the engine, warm or cold, without touching gas pedal.............it should surge to above 1,500rpms then drop to "target temp" RPMs based on coolant temp
This is because with Key on the computer boots up and OPENS the IAC Valve all the way for startup
When engine is above 400rpms(started), computer closes IAC Valve to set "target idle"

Could be previous own replaced Motorcraft IAC Valve with a 3rd party IAC Valve these don't play well with Ford computers
Motorcraft or Hitachi brand IAC Valves are the only ones that will work reliably with Ford system
Better to get a used Motorcraft IAC Valve at wrecking yard than new 3rd party IAC Valve

I would expect 1999 computer to set a low RPM code if IAC Valve was not responding as it should
You have no CEL(check engine light) but can you have the codes checked, could be some pending low RPM codes which would mean computer is "sane"
CEL doesn't come on unless a pending code is consistently repeated, and computer "remembers it"

You could clean IAC Valve, not hard to do
While its off
Turn key on
Look inside IAC Valve and watch the valve
Plug in its 2 wire connector
Valve should move open, it only moves 3/8" but should move
Then unplug connector, it should close
Repeat until you are satisfied its moving or NOT moving(key MUST be ON)


There is an anti-diesel screw on the throttle linkage, "looks like" an idle screw, it isn't, lol
BUT...........
Have engine fully warmed up and idling, AC OFF
Unplug 2 wire connector on IAC Valve, RPMs should drop to anti-diesel screw setting for throttle plate, about 500-600rpms
IF engine stalls then reconnect IAC Valve, and turn anti-diesel screw clockwise a full turn
Restart engine
Repeat test
Unplug IAC valve and RPMs should drop to 500-600, if higher or no drop turn anti-diesel screw counter clockwise to reduce RPMs so engine is not stalling but can idle, turn AC on and readjust as needed
Plug IAC Valve back in and RPMs should go to 750-800, 4cyl engines vibrate if idle is too low because they only fire every 180deg of crank rotation so they need a higher idle than a V6 or V8 engine

You are doing this to prevent engine from actually stalling when either computer or IAC Valve goofs up, because we don't know which one is causing it
 
Last edited:

MikeG

Well-Known Member
Joined
Jul 15, 2020
Messages
1,353
Reaction score
752
Points
113
Location
central Texas
Vehicle Year
1997
Make / Model
B4000
Engine Type
4.0 V6
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
2"
Tire Size
235/75r15
Reads like a vacuum leak, if the above doesn't address it.
 

1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
I wish I would have read this before delving into the throttle body cleaning, but it needed to be cleaned for sure. AIC apparently was replaced at some prior time [going by the appearance, evidence of being removed in past and no Motorcraft etching.] I gave it a cleaning along with throttle body last night, and am up this morning to put it together with new gaskets that just came in. I get no movement of AIC after the process you described (with key on) I tried un-plugged and re-plugged in a number of times to be sure with my glasses on (lol) and flashlight right in there to see...zero movement of plunger or anything. Now, with engine warm [and at idle with no loads] It's now running consistently at a relatively high idle [steady at 900 RPM] <--(after the cleaning,) and occasionally "hunts" for idle and wobbles a bit, but generally steady at 900. Looks like I need to go for a new Motorcraft IAC. Hard to find the Motorcraft for that year. Really appreciate the advice and will update.
 

Attachments

Last edited:

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Do you have a HIGH idle, 1,100+ rpms after COLD start?

And then slowly drops over the next few minutes to the 900 rpms level as engine warms up, this means the computer has some control of IAC Valve
 

1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
Do you have a HIGH idle, 1,100+ rpms after COLD start?

And then slowly drops over the next few minutes to the 900 rpms level as engine warms up, this means the computer has some control of IAC Valve
I'll have to wait until fully cooled down to verify (as I've been running it lately-in Florida:cool:) to verify that. I will try that later (without tapping the gas pedal) and see.
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Tapping gas pedal wouldn't matter, there is no "high idle cam" on fuel injected engines like a carb had
Computer sets idle base on engine coolant temp from ECT sensor

If tapping the gas pedal changes the idle then could be you have a problem with throttle plate sticking open a bit or weak return spring
 

1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
UPDATE March 14, 2021: As mentioned, the throttle body and IAC was cleaned and the next day I had the idle running high (900 rpm.) The high rpms were an additional new development. To answer what RonD asked,
a cold start up has an initial run up to 1,500rpm and DOES gradually going down to 900 as it warms (indicating "computer has some control of IAC valve.") However, I did NOT see plunger move when plugging in the freshly cleaned, but old IAC (with key on,) so I got another IAC (from well known on-line parts supplier,) but it was the wrong one, and I'm wondering if is even Motorcraft although it was in a Motorcraft box. It needs to have the plug at 90 degrees, and the plug would not fit to even test it.
Note that unplugging the freshly cleaned, but old IAC with engine running does drop the idle down to 600rpm.
It appears that I uncovered something else by cleaning the throttle body and IAC. I again verified the plenum is on secure and no vacuum lines off. I have taken it out for a few drives and it will sometimes stay at high rpm and then eventually settle at 900. It's drive-able (standard 5 speed.) Perhaps not enough power getting to IAC? I think I need a proper scan.
 

Attachments

Last edited:

tomw

Well-Known Member
U.S. Military - Veteran
Joined
Aug 15, 2007
Messages
1,613
Reaction score
46
Points
48
Location
toenails of foothills NW of Atlanta
Vehicle Year
1985
Make / Model
ford
Engine Type
2.3 (4 Cylinder)
Engine Size
lima bean
Transmission
Manual
2WD / 4WD
2WD
My credo
vertical and above ground
I have not seen an IAC actually move when power is applied, etc. They work different than I expect, having a 'duty cycle', which means power is applied/removed at a specific frequency. Apparently that positions the spool inside
properly.
If you get a good "Cold idle", with higher rpm cold that drops off, and a steady idle when the A/C load is added, and it doesn't stall coming to a stop, your done. Don't bother with spending more on a new item as it should do just the same.
tom
 

1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
I have not seen an IAC actually move when power is applied, etc. They work different than I expect, having a 'duty cycle', which means power is applied/removed at a specific frequency. Apparently that positions the spool inside properly. Ok, I didn't know that(y)
If you get a good "Cold idle", with higher rpm cold that drops off, and a steady idle when the A/C load is added, and it doesn't stall coming to a stop, your done. Don't bother with spending more on a new item as it should do just the same. <--Yes, all that is true, except it's running too high rpm's now (consistently 900rpm.) Also, I'm not completely sure it is NOT stalling since it's intermittant, but hasn't happened yet. Thanks for reply!
tom
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Yes, IAC Valve gets battery voltage on the red wire with key on, then OTHER wire goes to computer, computer uses PWM(pulse width modulation) to vary the ground connection, which is the same as varying the 12volt side

And what happens to 900rpm idle when you unplug the IAC Valve?
Does it drop to 500 or does engine stall, either is good, means no vacuum leak

Yes, IAC Valve may not move in a static test, thats because its movement can be based on 18" of Vacuum pressure pulling on it
You can emulate that pressure by pushing valve with key on, and then with it unplugged
 

1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
Yes, IAC Valve gets battery voltage on the red wire with key on, then OTHER wire goes to computer, computer uses PWM(pulse width modulation) to vary the ground connection, which is the same as varying the 12volt side

And what happens to 900rpm idle when you unplug the IAC Valve? <--idle goes from 900 to 600rpms when unplugged while running and throttle linkage stops at anti-deisel screw as you mentioned
Does it drop to 500 or does engine stall, either is good, means no vacuum leak<--and does not stall.

Yes, IAC Valve may not move in a static test, thats because its movement can be based on 18" of Vacuum pressure pulling on it
You can emulate that pressure by pushing valve with key on, and then with it unplugged How do I push valve (a thin screw driver and press it in from an angle?) Aside from a new IAC
looks like a proper scanner test may be in my future. Thanks so much for reply and let me know if you have any ideas on further tests to rule out IAC.
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Then computer is setting the 900 idle, could be requirement for emissions in that year
4cyl engines get a vibration below 750 or so anyway, because a cylinder only fires every 180deg of crank rotation

That's where auto stop/start came from
Idle is a big polluter, has to be Rich or engine will overheat
Every year the idle emissions tests got harder and harder to pass so idle got higher and higher, higher RPMs means more cooling so leaner mix
Then car makers simply had to stop the engine to pass the idle tests
Auto stop/start was born
 

1999Mazda Central Florida

Member
U.S. Military - Veteran
Joined
Jan 26, 2017
Messages
48
Reaction score
10
Points
8
Vehicle Year
1999
Make / Model
Mazda
Engine Type
2.3 (4 Cylinder)
Transmission
Manual
Tire Size
Michelin LTX M/S P235-75R15
Then computer is setting the 900 idle, could be requirement for emissions in that year
4cyl engines get a vibration below 750 or so anyway, because a cylinder only fires every 180deg of crank rotation

That's where auto stop/start came from
Idle is a big polluter, has to be Rich or engine will overheat
Every year the idle emissions tests got harder and harder to pass so idle got higher and higher, higher RPMs means more cooling so leaner mix
Then car makers simply had to stop the engine to pass the idle tests
Auto stop/start was born
Ok, that's interesting...it could be that cleaning the throttle body set things as it should have been all along, but 900? I also noticed (after warm up and driving) it will go to noticeably high idle (like 1,200--1,500 approx)
and stay there for about 15 secs then go back to 900 (which it has been since the throttle body cleaning.) BTW, the IAC I got was the wrong one (I ordered the one with 90 plug as is the EOM, but was sent one with straight plug, and they don't have the correct one by Motorcraft for my 1999 B2500) so I am unable to use it and it is to be sent back for a return. Wish I had a spare IAC to rule that out...but looks like computer is controlling the IAC to some degree.
 

Mightyfordranger

Well-Known Member
V8 Engine Swap
Joined
Apr 22, 2014
Messages
1,029
Reaction score
156
Points
63
Location
Ohio
Vehicle Year
1989
Make / Model
Ford
Engine Type
2.9 V6
Engine Size
2.9
Transmission
Manual
2WD / 4WD
4WD
Total Lift
3in
My credo
Clean your room before you criticise the world.
Ok, that's interesting...it could be that cleaning the throttle body set things as it should have been all along, but 900? I also noticed (after warm up and driving) it will go to noticeably high idle (like 1,200--1,500 approx)
and stay there for about 15 secs then go back to 900 (which it has been since the throttle body cleaning.) BTW, the IAC I got was the wrong one (I ordered the one with 90 plug as is the EOM, but was sent one with straight plug, and they don't have the correct one by Motorcraft for my 1999 B2500) so I am unable to use it and it is to be sent back for a return. Wish I had a spare IAC to rule that out...but looks like computer is controlling the IAC to some degree.
I drive a 99 2.5L ranger should be the same thing. Only prob is I don't have a tach. But I can get my live data scanner back from my friend and gather info for you if you'd like? Also if you can't find a genuine motorcraft IAC I can pull one from my local yard and check its function off my truck then Mail it to you.
 

Sponsored Ad


Sponsored Ad

Staff online

Today's birthdays

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Truck of The Month


Kirby N.
March Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top