Slow cold starting, rough idle, then runs fine after 15 seconds???

i've searched the forums & can't find the answer...

i turn the key from a cold start & my XJ takes at least 5 seconds to fire up (no problem turning over). once it starts, the idle is rough for about 15 more seconds. if i put it in gear during this time, it feels like it's going to stall, but doesn't. after this time, it "clears up" & runs fine...& usually starts fine once it's warm.

i installed an optima yellow-top & Accel tune up kit a few months ago thinking that would solve the problem but it didn't. i used sea foam in the gas tank & intake, that didn't solve it. i did notice that the throttle body had carbon built up on it (will clean it this weekend). what could it be?

i'm about ready to bring it to the stealership because i need it running smooth for the winter that's on the way up here! thanx



eric
99 Cherokee Classic - Flame Red Clear Coat, 4.0L I6, AW4, Selec- Trac, Up Country Suspension Group, Skid Plate Group, Trailer Tow Group, ABS, & every other available Classic options except block heater. Optima Yellow-Top, K&N Filter, Sylvania Silverstars, CATZ XLD Driving/Fog Lights, "Trail Rated" Badge

03 New Beetle Turbo S - Uni Red, 1.8T, 6spd.

I have similar problems. Although the car starts pretty ok it runs like a diesel for a while (and sometimes it runs fine) and starts running fine again when it is warmed up. Appears as if the timing is off or one off the injectors is not working for a bit. Just took the intake manifold off (had to replace the exhaust manifold) and it was pretty 'carbonized' inside. Will put some cleaner in the fuel to see if that helps. Maybe one of the injectors is dirty. Will keep you informed on progress and would love to hear what you come up with.

A leaky injector that dumps a load of raw gas in the cylinder can cause this symptom. It can also take out a set of rings pretty quick if not remedied.

Put a fuel pressure gauge on the rail. Monitor the pressure after the engine is shut off. The pressure should hold.

Alternatively, start the engine. Run it only for a second or two. Shut it off. Pull the plugs and look for a wet or fouled plug.

Thanks for the idea. Since I have just replaced the exhaust manifold I also had to depressurize the injectors. I was suprised that there was no pressure left on the system when I did that. Now it all starts to make sense. Leaky O-ring seals around the injectors!

Ok, let's say that's the problem, then I run into the next problem. When I took off the intake manifold last time I left the injector rail installed. This was not just convenience (although it turned out to be quite convenient) but for the fact that I couldn't get the injectors to come out. Is there some sort of trick for that? I rocked and pulled but with moderate to strong pull (I didn't feel confindent enough to really put all my weight on it) they wouldn't come off (yes, I did take out the injector-rail 4 bolts).

So if it's a leaking injector seal then I would simply replace the o-ring on the injectors (say that I did get them out) and re-install them? That would be great and this makes a lot of sense. So do you have a thought on why the engine runs so much better when it warms up?

Can I get these O-rings at any autoparts shop or do I go to the dealer?

Thanks, I am starting to feel better about this already!

I just got a set of o-rings last weekend at advances auto for under 12 bucks.

The leak that Old Man is talking about will be internal, the nozzle of the injector is leaking ontop of the piston, puddling fuel and soaking down you cylinder walls, not good. The external "O" rings seal the fuel from leaking out onto you man. causing a fire(rail side) and to seal in compression(manifold side).

I forgot to add: Check your oil, if it smells like gas you probably have some leaky injectors.

engine temp sensor? (the one in the jacket, unless its only the renix)

Also the upstream o2 sensor, bad readings until it starts to heat up, mine does that, gotta let it run for a few mins to clear up, then it runs fine.

Thanks for the advice! Also, thanks for pointing out my misunderstanding with respect to the leaking injector. I will have the pressure on the fuel system checked by a mechanic. I don't have the tools/experience to do that myself.

I have two questions with respect to the other remarks:

1) Where are the temp unit and upstream O2 sensor located?
2) How do I test that they do or do not work properly?

Thanks, appreciate your help!!

Tim

MAT sensor(Manifold Air Temp) located in the intake,the little sensor bulb can be coated with crud from the intake air,remove and clean with carb cleaner.
The temp sensor for the comp is in the thermostat housing,this is not the problem unless your motor heats up in 15 sec.O2 sensor is located in the down pipe in the exhaust,close by the oil pan.Again this doesn,t have any bearing on your problem until the engine reaches 150-180* and goes into closed loop mode.
Wayne

Thanks Wayne, the O2 sensor I saw when replacing the exhaust manifold, thanks for that one, will not touch that for now then. I also need to clean up the idle air controller since it doesn't high-idle at startup anymore (that's more recent and is -- by my knowledge-- not related to the rough, dieselish cold run). Will try and locate that MAT with my Haynes in hand and clean it up. Makes sense that the dirt has gotten to that sensor as the same dirt seems to interfere with the high-idle air controller. Will through in a bottle of Techron asap. I just got this car and the previous owner has so far not impressed me with his prudence in car maintenance so it has probably been a while since it had a cleaning. --Tim

The MAT sensor is located on the intake manifold,in the same row as several other vac ports and such.You must remove to clean as the fuel does not go into the intake except directly at the valve.FSM says to use teflon tape on the threads when you replace it.
Wayne

Got it. Will do!

Ah ha! So the search feature DOES work!

Mine is having similar symptoms that just developed yesterday. I'll crank it up on a cold start (say after sitting overnight) and it takes a long time to crank. At first I thought that I didn't let the fuel pump prime the system long enough. So today I let the fuel pump run for a good 30 seconds before I tried to crank it and it had no effect. Still took about 5-7 seconds of cranking. Once it does fire up, it sputters and runs horrible for about 5-10 seconds, then clears up and runs great. I'm not really smelling any gas, indicating a running rich/flooding out issue, but it's hard to tell at this point. After the 5-10 seconds of running like crap, it straightens out and runs great. Once it's warm and I try to fire it up again, the problem doesn't happen.

I'm also not getting a CEL....atleast not yet. I don't think it's acting stupid long enough for it to trip the light to come on.

I woulnt have a chance to check fuel pressure or get any readings off any sensors untill atleast Saturday.

Did you ever figure out what the problem was with yours? Possible causes i'm thinking at the moment are:

-Fuel Filter/Pump
-CPS
-TPS (although new, I havent ruled it out yet)
-Possible leaking injector (which i'm hoping is not the case)

Am I correct in thinking that if it were a leaking injector, one would smell unburnt fuel coming out of the exhaust, along with possibly some black smoke? If this is true, i'll have my buddy stand behind the Jeep tomorrow when I crank it up and look/smell.

Any advice is greatly appreciated. I'm taking it to the body shop Monday morning where it's going to sit for 2 weeks while they fix the damage from the accident. Would like to have an idea of whats wrong before I bring it down there, that way I can give the guys a heads up at the body shop so that when they're moving it around the lot they don't really screw something up, and also so I know what I need to look at replacing when I get it back.

Specs are a 99, 4.0, AW4, about 92,600K.

Things I have replaced recently due to other issues/preventative maint.
-Battery (about a year ago)
-TPS (back in Dec.) (TB was also cleaned thoroughly while I had it off changing the TPS)
-Full tune up about 20K ago. Was planning on doing another around the 100K mark.


I am also considering adding a can of seafoam on the next tank. I havent run a can through in about 10K or so....

Hi guys , first time poster and Jeep owner .

I was using the search function and saw this threrad. As I was reading the last post , mine is doing the same thing . It really doesn't want to start when it's cold . I just bought it a week ago , and 3 days later the water pump seized .

I had that fixed , and since about 3 days after I got it back from the shop , it started having this problem with not wating to start . If I push the gas a little and mess with it , it finally will .

This is a 93 Country , BTW , with a 4.0 . After it starts once , it's fine the rest of the day .

Any ideas on this specific problem ?
(Jeep is all stock , BTW .)

I tried hooking my scanner up to it today, and the coolant temp according to the scanner was correct. After sitting for 24 hours, I fired it up this evening and it was showing 66*, which is about what it was outside at the time (give or take a degree or two).

Interestingly enough however, it's acted up every single day this week...except yesterday and today. It's still got a long crank time, but as long as it's still running good I can live with that for now. It will be interesting in about two weeks when I go to pick it up from the body shop as to how well it's running.

I'm going through the same issue, I've been using the search function and have come across a couple of threads

http://www.naxja.org/forum/showthread.php?t=899585&highlight=rough+start

http://www.naxja.org/forum/showthread.php?t=898771&highlight=rough+start

http://www.naxja.org/forum/showthread.php?t=906529&highlight=rough+start

But has anyone check plugs? I've recently changed my exhaust manifold, had majorly rough idle and at random times it would do the whole "long crank/don't wanna run right unless foot is on gas" for a while. Once it's warm it's fine. When I get home from work today I'm going to check my plugs and see if it has some sort of carbon buildup or something similar. I didn't disconnect the fuel line when doing the exhaust manifold... nor do I have any means of testing it (no guage). In me trying not to start another thread, has anyone gone any further with this issue and possibly figured something out?

ndangrd said:

i've searched the forums & can't find the answer...

i turn the key from a cold start & my XJ takes at least 5 seconds to fire up (no problem turning over). once it starts, the idle is rough for about 15 more seconds. if i put it in gear during this time, it feels like it's going to stall, but doesn't. after this time, it "clears up" & runs fine...& usually starts fine once it's warm.

i installed an optima yellow-top & Accel tune up kit a few months ago thinking that would solve the problem but it didn't. i used sea foam in the gas tank & intake, that didn't solve it. i did notice that the throttle body had carbon built up on it (will clean it this weekend). what could it be?

i'm about ready to bring it to the stealership because i need it running smooth for the winter that's on the way up here! thanx



eric
99 Cherokee Classic - Flame Red Clear Coat, 4.0L I6, AW4, Selec- Trac, Up Country Suspension Group, Skid Plate Group, Trailer Tow Group, ABS, & every other available Classic options except block heater. Optima Yellow-Top, K&N Filter, Sylvania Silverstars, CATZ XLD Driving/Fog Lights, "Trail Rated" Badge

03 New Beetle Turbo S - Uni Red, 1.8T, 6spd.

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I had the exact same problem. I replaced my fuel pump which fixed it for awhile. When the problem came back i ran fuel injector cleaner through it for 3 fill ups in a row and now she starts up like shes supposed to.


-Aaron

Mine has the exact same symptoms, but mine is a 5 speed. Cold start is hard, idle is rumbly for a short time, then it clears up. When the engine is started warm, the problem magiacally disappears. (1990 Renix)

I ran the fuel pressure tests as outlined in the FSM and all was good. With the fuel pressure regulator disconnected, pressure was around 32 psi. With it hooked up, it was around 41. I turned the engine off and it held the 41 psi for 10 minutes, then I had to go because my friend was closing his repair shop early for a change on Saturday.

Any other new findings with this problem?