idles too fast with the air charge sensor connected

[greaseyfingers]

my 87 ranger's 2.9, usually, idles between 1100-1500 rpm's when the air charge sensor is connected...

if I disconnect the air charge sensor's plug in plug, it will idle down, nicely...

all the sensors have been replaced, new IAC, new spark plugs, new ignition wires, new air cleaner, new fuel filter, no vacuum leaks, all electrical connections seem to be good and intact... the engine's throttle cable isn't sticking, either...

I haven't replaced the distributor's ignition module, yet... I don't think that would be causing the engine's high idle problem, do you, or could it ??

the one thing I haven't done, yet, is to replace my transmission's fm145 neutral switch, which has two wires going to it, that are broken off, at the very base, of the neutral switch... so, I can't splice them back together, again...

I don't know how these wires managed to get broken off there... but, that's how it was, when I bought my ranger from the previous owner...

I plan on replacing this neutral switch, whenever I'm able to get one... however, most older vehicles, around here, have been getting crushed, these last few years, being the price of scrap iron is as high, as it is...

if it's possible this non connected fm145 tramsmission's neutral switch is, in fact, causing my ranger's 2.9 high idle... why would disconnecting my air charge sensor, make the engine idle down, nicely, to around 900 rpm's...

if I was to leave the engine's air charge sensor disconnected, to keep my idle down... would that cause any issues and concerns, with my engine's performance and depenability...

what do you all think, is causing my engine's high idle problem, as explained...

 

[IMenriched]

my 87 ranger's 2.9, usually, idles between 1100-1500 rpm's when the air charge sensor is connected...

if I disconnect the air charge sensor's plug in plug, it will idle down, nicely...

all the sensors have been replaced, new IAC, new spark plugs, new ignition wires, new air cleaner, new fuel filter, no vacuum leaks, all electrical connections seem to be good and intact... the engine's throttle cable isn't sticking, either...

I haven't replaced the distributor's ignition module, yet... I don't think that would be causing the engine's high idle problem, do you, or could it ??

the one thing I haven't done, yet, is to replace my transmission's fm145 neutral switch, which has two wires going to it, that are broken off, at the very base, of the neutral switch... so, I can't splice them back together, again...

I don't know how these wires managed to get broken off there... but, that's how it was, when I bought my ranger from the previous owner...

I plan on replacing this neutral switch, whenever I'm able to get one... however, most older vehicles, around here, have been getting crushed, these last few years, being the price of scrap iron is as high, as it is...

if it's possible this non connected fm145 tramsmission's neutral switch is, in fact, causing my ranger's 2.9 high idle... why would disconnecting my air charge sensor, make the engine idle down, nicely, to around 900 rpm's...

if I was to leave the engine's air charge sensor disconnected, to keep my idle down... would that cause any issues and concerns, with my engine's performance and depenability...

what do you all think, is causing my engine's high idle problem, as explained...

Well...it seems you have done a lot of work.....by disconnecting the air charge sensor & you get a better/proper idle...that tends to make me think that it is bad...

what codes are you getting?
have you checked for vacuum leaks???...& don't for get about the brake booster and the cruise control, if you have it.

sounds like your on the right track.

 

[holyford86]

if the sensor is out of range (too cold) it will give you a high idle. I have had that problem ever since i bought my truck. once it gets above 40 degrees out the idle will drop right down to 900 rpm. Unplugging the sensor makes the computer run off of a preset curve and that's why your idle drops.

 

[Jspafford]

Ditto, it sends the computer into limp mode and it usually ignores the rest of the sensors and runs off a default setting.

 

[Natedog]

Well...it seems you have done a lot of work.....by disconnecting the air charge sensor & you get a better/proper idle...that tends to make me think that it is bad...

what codes are you getting?
have you checked for vacuum leaks???...& don't for get about the brake booster and the cruise control, if you have it.

sounds like your on the right track.

X2 and don't forget the little plastic elbow that connects the vacuum hose to the brake booster...mine was split at the mold line from when it was made and looked fine until I really looked very closely at it.

Pull codes and post back.

 

[greaseyfingers]

Well...it seems you have done a lot of work.....by disconnecting the air charge sensor & you get a better/proper idle...that tends to make me think that it is bad...

what codes are you getting?
have you checked for vacuum leaks???...& don't for get about the brake booster and the cruise control, if you have it.

sounds like your on the right track.

now, the engine idles high, again, even while the air charge sensor is left unplugged...

before, when I would unplug the air charge sensor, the engine would idle, nicely, as it should... for some reason, now, it won't, even idle down, while leaving the air charge sensor unplugged...

there have been no vacuum leaks detected, anywhere... as far as I know, the the brake booster seems to be ok...

Engine Computer Trouble Codes -

KOEO Codes
67 - neutral drive switch open or manual lever position sensor out of range or neutral pressure switch closed...

Memory Codes
41 - No exhaust Gas Oxygen detected - always indicating lean...
33 - EGR valve closed / erratic or has insufficient flow...

KOER Codes
12 - Cannot control RPM during self check or Idle Speed Control Problem...
41 - No Exhaust Gas Oxygen switching detected - always indicating lean...

 

[greaseyfingers]

X2 and don't forget the little plastic elbow that connects the vacuum hose to the brake booster...mine was split at the mold line from when it was made and looked fine until I really looked very closely at it.

Pull codes and post back.

now, the engine idles high, again, even while the air charge sensor is left unplugged...

before, when I would unplug the air charge sensor, the engine would idle, nicely, as it should... for some reason, now, it won't, even idle down, while leaving the air charge sensor unplugged...

there have been no vacuum leaks detected, anywhere... as far as I know, the the brake booster seems to be ok...

Engine Computer Trouble Codes -

KOEO Codes
67 - neutral drive switch open or manual lever position sensor out of range or neutral pressure switch closed...

Memory Codes
41 - No exhaust Gas Oxygen detected - always indicating lean...
33 - EGR valve closed / erratic or has insufficient flow...

KOER Codes
12 - Cannot control RPM during self check or Idle Speed Control Problem...
41 - No Exhaust Gas Oxygen switching detected - always indicating lean...

 

[holyford86]

well, a faulty o2 sensor may cause a high idle, the EGR problem could as well. some info about your truck would be a good idea, things like year and transmission type would be helpful.

 

[greaseyfingers]

well, a faulty o2 sensor may cause a high idle, the EGR problem could as well. some info about your truck would be a good idea, things like year and transmission type would be helpful.

I've replaced the o2 sensor with a new bosch 02 sensor... I've, already, taken the EGR valve off and cleaned it, so it opens and closes...

after doing this, my engine still runs the same, with a high idle...

do you think there's a chance that the distributor ignition module could be causing this problem...

sometimes, the engine runs really rough, also, like it's missing...

my ranger is a 87 4x4, model STX, with a 2.9 and a fm145 5 speed tranny...

 

[mikediesel]

mine is doing the same thing i have code 41 koer and just got code 18 koeo i was wondering the samething about the ignition module my truck is an 86 4x4 but a 2.3l 5 speed idle is around 8-900 specs are 675rpm

 

[BradS]

Not trying to take your thread, but mines doing the same thing. if i unplugged my AIC Valve, would it harm anything if i drove it like that till i Have more time and money to work on things, If that fixes it of course?

 

[cleat]

Hi;

With any Ford I have worked on a high idle is almost always caused by a bad TPS. This will be real evident if when it is idling high and you shut the truck down and immediately resart it and the idle is normal. Other than that try cleaning the IAC and throttle body and also listen and check for vacuum leaks.

Cleat

 

[Jspafford]

Unplugging the IAC will most likely result in the engine dying.

 

[greaseyfingers]

Hi;

With any Ford I have worked on a high idle is almost always caused by a bad TPS. This will be real evident if when it is idling high and you shut the truck down and immediately resart it and the idle is normal. Other than that try cleaning the IAC and throttle body and also listen and check for vacuum leaks.

Cleat

when my 2.9 engine is idling high and I shut the truck off, after the engine has warmed up, and immediately restart it, the engine will usually idle down, somewhere, between 900 to 1,000 rpms.. I have, already, replaced my TPS with one from the junkyard from a 88 ranger with a 2.9, unless that one is bad, too, or isn't exactly the same one, as is supposed to be used on my 87 ranger with a 2.9..