irratic idle when engine is cold

[iLoveMyExploder]

1993 exploder 4X4. I just bought this truck the other day. I know nothing of its history. I went and started it up today and it had erratic idling when it was cold. but once it is warm, it idles normally.

the RPMs fluctuated between the normal idle speed and maybe up to +500 RPM at the highest surge. frequency and RPM speed exactly the same every time. when it idled high- it lasted for one maybe two seconds, idle went back down to normal for a second or two then idled up again. I didn't stop-watch the timing on this, but it seemed steady the whole time. it did this over and over again for 3 to 5 minutes until it warmed up some. and once it warmed up- it acted normal from then on.

I looked at the vacuum lines, and they all looked like they are in decent condition, some of them are brand new. I already know the engine idle speed is non-adjustable from its factory setting.

any ideas why it does this?

thanks in advance for comments

PS: possibly related problem?... when it runs awhile, and after its hot... if it sits for a long time (such as while stopped and waiting for a light to change), the RPMs lower... it will bog down a little bit but not so low that the engine quits running. possibly related? or is this a different issue?

 

[natenkiki2004]

When the engine is warmed up, do a KOER test and see what comes back. Hopefully the cold idle issue is something that the computer is compensating for when hot and will throw a code for it.

 

[iLoveMyExploder]

When the engine is warmed up, do a KOER test and see what comes back. Hopefully the cold idle issue is something that the computer is compensating for when hot and will throw a code for it.

ive been reading a lot on threads on here and learning more about my truck. I keep seeing this KOER test and code thing you just mentioned. what is that?... I don't have any special tools... where can I go to have the tests done? ... I took it to autozone, but they said they can only do the computer tests on cars 1996 and newer.

 

[natenkiki2004]

ive been reading a lot on threads on here and learning more about my truck. I keep seeing this KOER test and code thing you just mentioned. what is that?... I don't have any special tools... where can I go to have the tests done? ... I took it to autozone, but they said they can only do the computer tests on cars 1996 and newer.

You'll find the info on KOER here. Basically, there's 2 wires near the blower motor in the engine compartment that you jumper together then turn the key on and start the engine. The check engine light will flash and tell you all the secrets of the world.

KOEO is key on engine off. KOER is key on engine running. 2 different tests.

The 1996 & newer thing is OBD-II that came out in 1996, a federal mandate to allow communications with the vehicles computers. It basically makes it easier to talk to the computer. Before that, the manufacturers did what they wanted and thankfully, Ford put in their own self-diagnostic system.

 

[iLoveMyExploder]

that makes sense.... thanks for the info

 

[iLoveMyExploder]

problem solved (i think...)

I saw in another thread about cleaning the MAF sensor. so when I went to walmart I found a little can MAF cleaner bundled with a little can of throttle choke cleaner. the MAF looked clean to the naked eye, but I cleaned it according to the directions on the can- twice. as for the choke- it WAS dirty! it needed cleaning bad. it was black as the night and thick as well. after it was cleaned, I could see metal again. the next day I went to start it up while it was cold- no erratic idling at all. my guess is the problem was the filthy choke, but it just as well could have been both the choke and the sensor. maybe this info will be helpful to someone

 

[natenkiki2004]

There is no choke on fuel injected engines That's the throttle butterfly. They do get dirty and need cleaned periodically.

I still don't understand why they get dirty. It's not from the hose that goes under the oil fill cap, that's the inlet for the crankcase. Air goes in there and is sucked back through the vacuum side on the other valve cover with the PCV.

Anyway, glad you made some progress on that.

 

[iLoveMyExploder]

I thought the thing that opened and closed to let air in was called a choke... but I guess I was wrong!

every time I get on here I learn something new- usually from you!! LOL