Cold Engine = Rough Running 90 Laredo 4.0L

[dogkatcher]

so .. 1990 cherokee laredo 4.0L, manual trans (bought it with 108k miles .. new plugs, rotor, wires, distrib done asap)

now 135K miles .. new cps 10k miles ago, fuel filter about same. fuel pump about 20k. tps was adjusted during cps (seemed ok)

starts up fine & idles fine (so it sounds) .. when 1st starting to drive it bucks as if not getting fuel .. thru 1st & 2nd gears, by the time I get into 3rd is slightly less noticeable until engine reaches top temp .. then its pretty much smooth sailing .. maybe once or twice I can barely feel this lack of power for a split second while cruising

Note: to give a more accurate description of whats its doing ... prior to problem ... when very low on gas & hit the curb dip leaving work, it does this for a very brief second, as if not getting fuel

I do get some blow-by .. I just changed oil & air filter .. still does this .. throttle body was cleaned not too long ago, still l ooks good

air intake sensor ? coolant sensor ? cold coil ?? cold or failing tps?

not sure, but its kind of annoying .. need to nip it in the bud

during summer I had issues of very high RPMs at start .. up to 2500, then would slowly relax .. sometimes just restarting it would take it back to a normal rpm

I dont have volt meters or anything hi-tech to test system. maybe someone has an answer before the paid mechanic has to probe the engine

[danielsatur]

Symptoms of a bad, or dirty Massive Air flow sensor (MAF/IACT).

[dogkatcher]

Originally Posted by danielsatur

Symptoms of a bad, or dirty Massive Air flow sensor (MAF/IACT).

so .. Im having a bit a trouble finding a part under that specific name

same as MAP sensor ? if so .. I bought a new one about a year ago (during the CPS screwin up pre-fix) ... the new Map failed in about 30 minutes, wouldnt even start again .. put old 1 back in & it fired right up

OR .. is it the intake temp sensor .. not sure of what you mean because I cannot find anything on it under that name .. I recognize it from forums .. but finding a part under auto parts stores is not working

[danielsatur]

OBD I system - fewer codes

1) Check the cold air intake + filter
2) Air Temp sensor
3) Air leaks on plastic duct work
4) What about egr gasket, or valve?
It could be running a little lean, the fuel/air mix is wrong during the cold condition.

[dogkatcher]

so .. tryin to find this gremilin still ... the problem became more random than just cold

changed the plugs (looked great for 25k miles), oil, air filter, fuel filter within last 2 weeks (battery 2 days ago)

no blow by in that 200 miles of new air filter

yesterday, I sprayed out a few of the small air tubes & the little metal piece in air box that goes to 2 tubes .. and one of those tubes goes to the front by radiator - attaches to a diapragm lookin thing on air intake & has a relay .. what is that ??

also, pulled the IAC out and wiped it down, no cleaner used

Now ... starts & idles around 900 rpm with cold engine .. after driving a bit & warm, it rpms around 1100 at idle, sometimes a bit higher

good thing .. it hasnt bucked like a bronco & my worries of a bad fuel pump or slipping gears are gone

& I noticed the outside air temp reading shows -88 F .. what did I touch ?? & what tells it the temp anyway ?? incoming air before airbox ?

is it a bad IAC ?? or is the air temp making it think its -88 F outside ? maybe the IAC is working now & the coolant sensor is bad? (makin it think its cold)

really confuzzled now

thinkin of gettin a junk yard TPS & IAC .. and see what happens .. what should I look for if I grab a used IAC ??

not sure where the air intake temp is located either .. still learning the 4.0..... haha

[dogkatcher]

well .. found out why the idle went berzerk into high rpms ... found a hose disconnected today .. theres a 3 way adapter into intake manifold (by TPS) .. 3 hoses attach (1 from fuel press. reg. .. 2 from egr) .. 1 going to egr was disconnected .. haha .. forgot to plug it back in when I cleaned it

so ... went to the ole JY today .. got a used IAC for $5, looked very clean considering I went thru about 10 motors .. all had filthy black crudded up IACs ... man, what a relief knowing my intake isnt that dirty

so.. cleaned the part up & cleaned the TB up a bit ... hasnt bucked like a bronco yet & the idle seems ok .. guess we'll see on the next freezing day how it acts .. going to buy a new vacuum harness next

also .. cleaned & seated the wire terminals to the fuel ballast resistor better, were kinda wobbly before .. maybe that was why I had some loss of power on bumpy roads

after the JY, i feel I have a very clean motor

[fredjacksonsan]

Well done. Vacuum is a funny thing!