Check Engine Light On -po174 when plugged few hours runs okay

[bryankeith]

Hi Everyone

Check Engine Light On.
PO174

Problems is when I start my vehicle up [1998 Explorer xlt 4.0L SOHC] in the mornings with a/c and other controls off, it runs rough, idle varies up and down, almost to stall, hard to control with throttle peddle, ,after warms up for a few minutes is seems to idle nicely.

Now when I plug the car in for several hours in the morning (say 15 degrees celcius) before starting it....it starts and runs great. But who wants to plug their car in during colder summer months.

During cold start idling with a/c or any other themperature setting ON (I think) the a/c compressor cycles...clicks on and off at short intervals. This really plays hard on idle -kicks down then up. Now it seems the A/C is on all the time even when the vehicle is on defrost...still cycles. I thought the a/c only works when the a/c or a/c max is on.

I have looked through all the dozens of posts and feel I could be doing many tests...so just thought I would run it by you pros.....))

Bought vehicle....a while back replaced filter was filled -very dirty....bought a scanner and got the code PO174... later up popped the check engine light...

Really need your help as I transport my son who has epilepsy and special needs coupled with my disability...it is important we have a good starting vehicle. Money has been tight so if I can fix it myself that would be cool.

Thanks for you help!!!!!!!

Bryan O

 

[bobflood]

Hi Everyone

Check Engine Light On.
PO174

Problems is when I start my vehicle up [1998 Explorer xlt 4.0L SOHC] in the mornings with a/c and other controls off, it runs rough, idle varies up and down, almost to stall, hard to control with throttle peddle, ,after warms up for a few minutes is seems to idle nicely.

Now when I plug the car in for several hours in the morning (say 15 degrees celcius) before starting it....it starts and runs great. But who wants to plug their car in during colder summer months.

During cold start idling with a/c or any other themperature setting ON (I think) the a/c compressor cycles...clicks on and off at short intervals. This really plays hard on idle -kicks down then up. Now it seems the A/C is on all the time even when the vehicle is on defrost...still cycles. I thought the a/c only works when the a/c or a/c max is on.

I have looked through all the dozens of posts and feel I could be doing many tests...so just thought I would run it by you pros.....))

Bought vehicle....a while back replaced filter was filled -very dirty....bought a scanner and got the code PO174... later up popped the check engine light...

Really need your help as I transport my son who has epilepsy and special needs coupled with my disability...it is important we have a good starting vehicle. Money has been tight so if I can fix it myself that would be cool.

Thanks for you help!!!!!!!

Bryan O

Since vehicle runs well once warmed up, I would look at engine temp sensor that PCM (computer) uses first. If PCM doesn't realize that engine is cold, it will not know to set controls correctly.

AC automatically works to dehumidify in the defrost settings; vent and panel/floor settings are only ones where AC not used. (Never have understood why Ford refused to include a separate switch to turn AC on/off like most other cars!!)

 

[bryankeith]

Appreciate the help Bobflood!!!!!!

Engine temperature sensor.....

So that means just by plugging in the vehicle the engine is warmed up enough to run smoothly upon cold start?

Concerning the a/c -so why is it that the a/c kicks in every 5-10 seconds? This is so strange...

O

 

[bobflood]

Appreciate the help Bobflood!!!!!!

Engine temperature sensor.....

So that means just by plugging in the vehicle the engine is warmed up enough to run smoothly upon cold start?

Concerning the a/c -so why is it that the a/c kicks in every 5-10 seconds? This is so strange...

O

That is my guess re engine temp sensor. P0171/P0174 are "lean" codes. When your engine is cold, the PCM needs to rich up the mixture for engine to run properly - if it thinks it's warm, it will lean it out and thus not have enough fuel in mixture to run properly when cold. "Unencumbured by knowledge" at this point, but it gives you a place to start.

Re the AC: Short cycling of the compressor is often a symptom of low refrigerant level. Again, a place to start looking.

 

[bryankeith]

thank you very much for your help.......will replace the part....I had it narrowed down to a couple things and this illiminates sooooo much....))

 

[drlower]

agree that the refrigerant level is most likely the cause of the compressor short cycling. as for the rough idle at start up the mass air flow sensor could also be to blame. the obd systems are often slow to pick up on maf problems and often just throw lean codes. there are many threads about how to clean the maf sensor that could be worth a shot.

 

[bryankeith]

cleaned the MAF several days back...but used to clear the code via disconnecting the battery I hear....suppose to clear the codes through the code reader....

maybe I should do it again through the code reader....

 

[drlower]

i also have always been told you need to clear codes through the code reader; however, disconnecting the battery has always seemed to work. could also try cleaning the plunger on the idle motor or replacing the throttle possition sensor. if you have a factory air intake still, check the heat riser tube on the passenger side exhaust manifold.

 

[bryankeith]

I think this site rules!

Nice to be able to get some tips from other owners or mechanics....

Thanks again!

 

[joe doe]

sounds like typical symptoms when the upper intake orings need replacing .
these orings are right under the upper intake ,they shrink with age and dont seal very well when cold allowing air to get by causing a lean code to be thrown .
when the engine warms up these rings swell and start sealing and your idle gets better .
this is why you have a bad idle on cold starts and it gets better as the engine warms up .

research your lean codes here on the forum and you will get the answers you seek .

 

[bryankeith]

thanks Joe Doe......

here is the question......

If you plug in your vehicle...that is block heater....for an hour and a half will that warmup the upper intake o rings to the point where the vehicle starts smoothly or, is it more likely that the engine temperature sensor is affected more?????????

Will be working on it this weekend! or see if I can get a mechanic to do it....

appreciate the help...

Bryan O

P|S was looking for leaks used propane torch...of course just the propane and vehicle never demonstrated any leaks or idle increase....maybe I never did it enough? lol...

 

[bryankeith]

:exp:

Update, my tinitus wasn't too bad the other morning and I could hear a slight hissing.... on the passenger side couldn't pin point it.....so went out bought myself a big cigar.....for the next morning...

So next morning I took off the left back vacumn hose and put my fancy air mattrass hose onto it and duck taped it up.....so no leaks..... lit up the ol cigar...hey, I never inhailed either...x-smoker....and with the engine cold in the morning I blew in 4 breaths of smoke while I aimed my large hallogen light around the engine...

Seemed smoke was coming out passenger intake manifold area/side all right.....around the middle fuel injector.....couldn't pin point it but the injector site had some moisture around it......might be a injector leak...o-ring..?????? Seems there is a plastic container in there too...loose....just moves around...what is that guys..?

Have a few more bucks to save up for the mechanic.....neck and back are bad....so when warm it runs not too bad..... guess this can harm the engine eh?????

hmmm.


edit: Missed out information: codes read: PO300, PO171, PO174