2.9L high idle.

[kyle1468]

I have a 88 ranger with 2.9l and it has a consistent high idle around 12-1500rpms runs fine except with a little lack of power but it just idles high I replaced IAC but didn’t change anything I tested TPS at idle shows .79 volts I don't have any codes. If I pull the spout connector out it idles fine around 800 rpm’s. Any idea of where to go from here. Thanks.

 

[RonD]

After engine is warmed up and idling high
Unplug the 2 wire connector on IAC Valve
If computer was causing the high idle then idle will drop to under 600rpms

If idle stays high leave IAC Valve unplugged and pull off one vacuum line at a time from the upper intake and plug the intake's port with finger
If idle stays the same then put that hose back on and try the next one
Start with power brake booster hose and then PCV Valve hose
Also check any ports with Caps, caps can crack and leak too, lol

If no ports show leaking, then you can spray soapy water around the warm engine, upper and lower intake, including throttle body
Engine will stumble if its sucked in
And worst case if you don't find a leak is the engine is cleaner, NOT on fire like if you used flammable fluid


Do you have a timing light?
If so check timing with warm engine and SPOUT disconnected, 10-12deg BTDC is what it should be
20-22deg BTDC with SPOUT connected

 

[kyle1468]

I will check that out when I get home. I do not have a timing light but I think I will go buy one as much as I could’ve used one throughout working on this truck how exactly should I go about checking timing? Should engine be at operating temp first when checking timing?

 

[RonD]

Yes, engine needs to be warmed up to set base spark timing


Gasoline engines need to be "choked" when cold, which means Richer Fuel mix, spark advance and higher idle
On carb engines that was done with a choke plate to restrict air flow which sucked in more fuel from the Jets, and a Cam on the throttle plate to hold idle higher, it also caused higher vacuum in the intake to change Spark's Vacuum Advance

With fuel injection the computer runs "choke mode"
A new sensor was added, ECT(engine coolant temp) sensor, a 2 wire, 5volt sensor, only used by the computer
Dash temp gauge still uses the 1 wire, 12volt Sender

If engine temp doesn't warm up, ECT sensor doesn't show warmer temp, within 5 min, the computer will set a code for that
And cold engine idle is usually no more than 1,100rpms on first start and then should drop fairly quickly to 650-750rpms on a manual trans within 5 min of run time

 

[kyle1468]

Yes, engine needs to be warmed up to set base spark timing


Gasoline engines need to be "choked" when cold, which means Richer Fuel mix, spark advance and higher idle
On carb engines that was done with a choke plate to restrict air flow which sucked in more fuel from the Jets, and a Cam on the throttle plate to hold idle higher, it also caused higher vacuum in the intake to change Spark's Vacuum Advance

With fuel injection the computer runs "choke mode"
A new sensor was added, ECT(engine coolant temp) sensor, a 2 wire, 5volt sensor, only used by the computer
Dash temp gauge still uses the 1 wire, 12volt Sender

If engine temp doesn't warm up, ECT sensor doesn't show warmer temp, within 5 min, the computer will set a code for that
And cold engine idle is usually no more than 1,100rpms on first start and then should drop fairly quickly to 650-750rpms on a manual trans within 5 min of run time

Okay I will do the tests when I get home for vacuum leaks and test the IAC and if that shows nothing I will go buy a timing light and check that out. I will get back with you about my findings. Thank you.

 

[RonD]

Check local craigslist

 

[kyle1468]

Okay so I found vacuum leak fixed it it idles for about20 secs good then starts to chug and idle low then die out starts right back up

 

[kyle1468]

Also when it starts to idle low you can hear a air sound like it’s trying to pull in more air then it will pick back up and idle fine or sometimes it will die out smells like gas a little when it does it like it gets to rich

 

[RonD]

Warm engine, unplug the IAC valve
Lets see if the computer is causing that because its not controlling the IAC Valve correctly

With no IAC valve, or Vacuum Leaks, the warm engine should idle at about 550-600 or so, barely running
There is an "anti-diesel" screw on the throttle linkage, looks like an idle screw but fuel injected engines can never have idle screws, that's why its called an "anti-diesel" screw, lol

If engine stalls with IAC Valve unplugged turn that screw in, clockwise, and restart until it can idle at 550-600
That would be the Factory setting, or should have been
And it should stay running that way until you shut it off or plug back in the IAC valve

 

[kyle1468]

Warm engine, unplug the IAC valve
Lets see if the computer is causing that because its not controlling the IAC Valve correctly

With no IAC valve, or Vacuum Leaks, the warm engine should idle at about 550-600 or so, barely running
There is an "anti-diesel" screw on the throttle linkage, looks like an idle screw but fuel injected engines can never have idle screws, that's why its called an "anti-diesel" screw, lol

If engine stalls with IAC Valve unplugged turn that screw in, clockwise, and restart until it can idle at 550-600
That would be the Factory setting, or should have been
And it should stay running that way until you shut it off or plug back in the IAC valve

It turned out to be the Map sensor because when I unplugged it it idle somewhat normal never stalled I had a old one I put back on and it works fine but truck still has low power when pulling hills and trying to keep up to highway speeds but I had to cut exhaust out to get transmission out I welded it back in place but has a decent leak didn’t know if that would be causing it or if maybe the map sensor I put back on is just on its way out too.

 

[kyle1468]

so I decided before I asked anymore about this I’d drive truck to work and it started fine drive okay low power on hills poor acceleration but over all drove okay it idles fine soemtimes then sometimes will start to idle real low and jump back up and idle fine and sometimes starts hard will fire up okay if you hold throttle wide open. Could this possibly be that old map sensor I put on or something else I am not 100% sure of what symptoms I’d get with a bad MAP sensor. But when it comes to hills truck just seems to have no balls and when it idles and then it decides to drop and idle real low it’s like the truck loads up with fuel and dies but starts right back up. Then will idle fine and maybe do it again 20-30 secs of idling

 

[RonD]

Vacuum gauge can tell you a lot about engine condition, $10 tool

And MAP sensor reads Vacuum in the intake so computer can calculate engine Load

Gasoline engines at sea level to 1,000ft elevation should run 18-21" of vacuum at idle
Low compression or bad spark timing will lower that
If vacuum is under 17" but steady then you will need to reset base spark timing first and if it doesn't come up then do a compression test

If needle is not steady at idle then partial misfires which could be spark related

If you raise RPMs to say 2,000 and hold it there steady while watching vacuum gauge
If vacuum is slowly going down then clogged exhaust
If slowing going up then clogged air filter/intake hoses

Lots more tests, but that's a start

 

[kyle1468]

Okay I will have to go get those tools after work I did test my map sensor voltage at work this morning I have 4.8v on power wire good ground but my signal wire sits at 2.5v I thought it was supposed to read close to 5 volts aswell when KOEO

 

[RonD]

MAP sensor will always show 2.5volts on signal wire with key on, that does mean it is powering up, not working but powering up

MAP signal is a Frequency signal carried on the 2.5volts
Some Volt meters have a Hz setting you can use

Chart here: https://www.aa1car.com/library/map_sensor_ford.gif

Hook meter to a ground and the signal wire
Key on/engine off, 0" vacuum, 159Hz
Engine at idle 18" vacuum, 109Hz
And that's about all you can test
You can REV engine with vacuum gauge hooked up, but hard to get a stable vacuum to compare

You really need a vacuum pump with gauge to test a MAP sensor thru its full range

 

[kyle1468]

MAP sensor will always show 2.5volts on signal wire with key on, that does mean it is powering up, not working but powering up

MAP signal is a Frequency signal carried on the 2.5volts
Some Volt meters have a Hz setting you can use

Chart here: https://www.aa1car.com/library/map_sensor_ford.gif

Hook meter to a ground and the signal wire
Key on/engine off, 0" vacuum, 159Hz
Engine at idle 18" vacuum, 109Hz
And that's about all you can test
You can REV engine with vacuum gauge hooked up, but hard to get a stable vacuum to compare

You really need a vacuum pump with gauge to test a MAP sensor thru its full range

I will have to get a vacuum gauge after work because my multimeter doesn’t have a Hz function I did start the truck at idle it’s showing 2.68 bolts but probably means nothing about the sensor so I will get a vacuum gauge after work and hopefully that will tell me more.