Techno Duck

Had this develop over the last few days. I thoughti t was related to the humidity and rain but it hasnt gone away. Its a really low, stumbling idle at cold start. Here are the main facts so far..

-No issues starting, does not crank any more than usual
-Cannot reproduce it with even a marginally warm engine (say idled for 3-4 minutes, shut off then restart).
-Pressing the throttle a bit and RPMS, go up, but still feels like its missing.
-It smooths out after ten seconds or so and stops completley
-Car drives fine.. no loss of power or anytihng like that.
-Lots of new parts all within the last 10k or so miles atleast...

plugs, wires, cap and rotor
DME temp sensor
FPR (probably less than 15k miles on it)
Cleaned injectors by Witchhunter
New airfilter
New ISV and vac hoses
Rebuilt throttle body

Any idea what can be causing this? The only thing i could think of is leaking injectors? But if the injectors were leaking wouldnt that cause the car to be hard to start?

I do have a leak in my exhaust on the crush ring that connects the catback to the cat...its been like that for over a year now (never got around to getting the car on the lift).

Ed 944T

I had a similiar problem when running 20-50W oil in cold weather, I changed it to 10-30W and the problem went away.

Techno Duck

I am running 20w50. I was planning on switching back to 10w40 for the winter in a week or two. Temps have dropped down to mid 70's or so... i hope thats the case!

arbeitm

Could be DME Temperature Sensor or a vacuum leak.

Yabo

or headgasket.

Oops, i didn't say that. just watch your coolant anyway.

rberry951

So something is not sealing properly, warming up and sealing it seems. Have you had the intake off recently? If so, check the torque on the intake bolts, and since you did work to the throttle body, check those as well. You say you replaced plugs recently, but I had to replace my plugs 'often' or else it would to that, or not start at all until I cleaned them or replaced them. Just for giggles, pull one out and look at it, or all of them, they're easy to get to...

Regards,
Russell

Techno Duck

DME temp sensor is new and only has about 10k miles on it, probably less than that. I need to check my records. I thought it was this also however the idle smooths out within 10 seconds or so which leads me to believe its another problem. I dont think ~10 is enough time for the coolant to get up to temp.

Headgasket...i dont think its this but who knows. I do loose coolant, albeit ive been loosing coolant ever since i changed the waterpump back in '05. Its been a super slow leak, figure one half a liter (one Poland Spring waterbottle) worth every 6-700 miles. I have no white smoke out of the exhaust, no coolant in the oil or vice versa. Also no problems with overpressurized coolant system. The leak has been so slow i cant detect it, i am thinking its burning off before it drips or shows up. Going to redo the waterpump when its time to do the belts again, another 10-15k miles to go.

I had the intake off and throttle body off the same time i did the DME temp sensor. Ill defenetley go over and retorque everything. Ill check the plugs tomorrow afternoon. I cant remember how many miles i have on them, but its defenetley not much i think a little more than 5k miles on them.

Thanks for all of the suggestions.

Yabo

Well hopefully it's just that. but i was losing coolant and never seeing drips, smelling it, etc for the first 8 months I had my car.. granted i was losing it a bit quicker than you say you are, but it would run on 3 cylinders or jsut rough for the first 20 second of runnign when cold, and never do it again until it sat for the night or at least 5-6 hours. I had no mixing either..

i'm rooting for it not being that though.

Techno Duck

Just pulled the plugs, yes at 10:30pm at night in the parking lot of my school..but heck the tool kit comes in handy . All the plugs look good, nothing out of the ordinary. Also checked the bolts on the intake manifold best i could with the allen key in the tool kit, the 4 out of the 8 i was able to check were all still tight. Will recheck the other four and the throttle body bolts if i can find a good set of allen keys tomorrow. Otherwise will wait until friday.

Kinda stumped here, any other suggestions or ideas? Cant think of anything else that would cause this.

Going to try and change my AFM friday back to my old one.. i doubt its this as i replaced it with a known good one (followed all test procedures on FRWilk's page)..but worth a shot i guess.

yellowline

Among other things, that's been a cause of bad idling for me.

AFM is a good idea. Have you retracked/soldered in a jumper wire if it doesn't have one? That did a lot for my car.

Techno Duck

I just took the car for a run around the campus, about .8 miles. Took it nice and easy.

No white smoke from the exhaust. After about one minute of driving i pulled over into a lot and popped the hood..took the coolant resevior cap off and no serious pressure buildup. Put my palm over the mouth of the tank and didnt feel any 'puffing' or surging.

I started the car up and no rough idle. I havent run the car since about 7pm and i did the same exact thing, just a quick run around the campus and shut the car down imediatley. I figure its sat about 4.5-5 hours. Maybe i jostled something when i checked the plugs. Will fire it up again tomorrow after lunch and see what happens..

PeteL

Look at the fuel pressure regulator. That was the source of my rough idle.

SchnellerUmsetzer

I assume that you did install a new O-ring on the rebuilt throtle body.

Techno Duck

Just an update on things...

I took a ride yesterday, probably 10 miles with minimal to no traffic. Ran great the entire way, no rough idle on start. I let the car sit about 5 hours and came back.. rough idle is back. Here is what i think. I depressurized the coolant system after my short jaunt around my campus two nights ago. Hence why there was no rough start when i started it up yesterday. I left the cooling system alone and pressurized when i got back, hence the cold start issue. So i would say its very likely to be the head gasket has probably a pinhole leak somewhere and is leaking coolant into one of the cylinders when the car sits. I am going to let the car sit overnight when i get home and start her up, if the rough idle is present.. ill imediatley shut down and pull the plugs and check the cylinders for antifreeze.

The ride home later should be interesting..hope it makes it the 25 miles. Ill have the triple A card handy and make sure my cell is fully charged.

Now to my question, is it absoltuley necesary to have the head decked (shaved) if i change the gasket? Also is it necesary to replace all of the headstuds? I ask about shaving the head because i have yet to find a machine shop in my area which i trust with something relativley big like this. I am thinking of just buying the rebuilt cylinder head from 944Online..but that turns a roughly $200 job (Gaskets and machine work) into a $600 job very quickly.

Techno Duck

Just another update.. car as been running fine. 25 miles home and a few runs around my area doing errands. Not overheating, loosing coolant, white smoke or anything like that. The car did still have the rough startup after i got home and restarted the car after an hour or so.

I just did a compression test as well. I am at sea level (Long Island NY). I did a dry test, engine was still hot enough to start to burn my hand if i left it on the intake manifold to long.. (oops!). All spark plugs out, throttle open for each test. I cranked it maybe 10 times or so for each cylinder..here are the numbers..

Cylinder 1 - 154 PSI
Cylinder 2 - 154 PSI
Cylinder 3 - 155 PSI
Cylinder 4 - 160 PSI

Now reading around these numbers look to be alright.. 160psi seems to be ideal i think? So what is the consensus, still possible for it to be a bad head gasket? Also i am using 20W-50 oil if that makes a difference. Also the engine has just under 90k miles on it.