How much dry gas?

[98XJSport]

Ok I have a 98 xj 4.0 auto. For the past week its been idling rough about 2 mins after I start it, no matter what the engine temp. is. As long as its sat more than 15 mins, it does this. Anything I do at the time seems to have no effect, its acting like there is a problem with the gas flow. Ive also noticed it doesnt do it as often or as bad when its above freezing. Thats been one day out of the last like 10. Ive started adding dry gas, but when do I give up on that and try cleaning sensors, etc? Ive added 5 little bottles that treat 10 gallons of gas each over the past 3 days. It hasn't changed much at all. Im hoping to get it in the garage at work and warm it up for a few hours and try another bottle, but at what point should I figure that the dry gas isn't going to help me? Thanks

 

[Colorado_XJ]

Yeah, I'd stick with exactly the manufacturer's recommendations for the quantity of dry gas (anhydrous isopropyl alcohol) to use. Basically, all it does is bond with the water and make it into a combustible compund. Too much of it will not do your motor any good. That's how it was explained to me. I would definitely have you OBD codes checked and start there. My '90 ran rough for a while, and it turned out to be a shot gasket on the intake manifold. But it could be anything (sensor, injector o-rings, fuel filter, plug wires, literally almost anything). The O2 sensors are notorious for causing all kinds of little annoying problems. But I would start with the OBD codes and work from there.

-Rich

 

[98XJSport]

Theres no check engine light going off. I have a new o2 sensor, and coolant temp. sensor as well. I don't have a removeable fuel filter, so I can't change/check that. Mainly im wondering how long to keep using it if the problem doesn't go away?

 

[Colorado_XJ]

The dry gas doesn't cure an ongoing problem, it's mostly a preventative measure. A little water in the fuel won't do much to the ignition, but it will caused ice to form in the lines, plugging them and causing a stall. Fuel itself freezes well below the temp that water does. It sounds like something else is going on. I'm still gonna recommend having a quality OBD scanner plugged into your XJ. There are many sensors that can screw your ignition up, not the least of which are your CPS, IAT and MAP. Someone here also had a rough idle and it turned out to likely be a stretched timing chain.

If you have gone through a tank of gas and the problem still persists, I would say it's a safe bet that moisture in your fuel isn't the culprit.

-Rich

 

[98XJSport]

So you can get codes pulled from obd-2 even though the check engine light isn't on?

 

[Colorado_XJ]

That's what I thought...I could definitely be wrong though. Regardless, it sounds like dry gas isn't fixing this problem. I'm sure some other folks have some ideas...

-Rich

 

[XJ Buzzard]

Have someone hook up a scanner and have them watch the data stream. Watching the O2 sensors, MAP, LTFT, STFT and the other sensors may give you a clue as to what is going on.

chris

 

[98XJSport]

Just an obd diagnostics scanner like a parts store lets you use for free? Or something more sophisticated?

 

[XJ Buzzard]

I believe it is going to have to be an actual diagnotice tool, like a Mastertech or Modis.

I wouldn't know about Auto Zone's tools. I was once told the HO2S that went bad was a hot water sensor. No more business from me.

A local shop may do it. At my old shop I had a preference for Jeeps and when they would come in I would do the initial diagnoses for free. You might get lucky and find a shop that could do it for a nominal fee. It may help eliminate some of the guess work.

chris

 

[98XJSport]

Most local shops around here would refer me to the dealer to get a scan like that. I would almost rather start replacing likely sensors that pay them what they would charge for the diagnosis and fix. I have a new coolant temp. sensor, so I know it isn't that. I will try today to get the MAT sensor out and clean that. Should inside the TB be black/soot covered from the butterfly down? I don't recall that it was before, I gave the tb a hosedown with carb cleaner. My O2 sensor is relatively new, but the snap that holds the wires broke and let them dangle against the driveshaft for a few hundred miles. Electrical tape seemed to fix it, but with this stuff going on im not 100% sure. Any suggestions?

EDIT: I put the jeep in the garage all day yesterday, and it did not stumble or do anything out of the ordinary for the drive home. But this morning the problem was back, a nice 5 degrees out. Thats the second time that it hasn't given me any trouble after keeping it warm. Could it be water freezing up the TPS?

 

[Cox89XJ]

When engine is cold, start engine and let run a few seconds. Turn off engine and remove spark plugs and check for water. I've had a similar thing happen twice on different vehicles and it ended up being a head gasket. What happens is a small amount of water leaks into the cylinder and when the motor runs a few minutes it drys itself out. It's not leaking bad enough for engine to miss due to low compression.

 

[gjxj]

look for an unusual amount of steam out the exhaust when its rough..
(obviously hard to judge when its real cold..)