Any thoughts?

I have a 90 model 4.0 L auto Limited XJ....its stock, for now, I love this car, and lately it makes this odd and weird thing that makes me C R A Z Y .....
ok.... Every time i start it i works diferently!!!...what i mean is :.... lets begin from idle... it may hold a normal and steady idle or it can do like it rumbles and almost dies...like 200 revs....
and if i give it some pedal...it starts to blow and bang... in the filter box...
If i stop the engine and re - turn the ignition key it may work ok...or the oposite....
Ok ...when driving now...in Overdriveor any other gear.....the car can go normaly even for more that 500kms if i dont restart it.. but if i do.....hell comes... it blows...bangs..and cuts off..more in lower revs.. and it only cleans... and runs good in higher...(imagine me in raffic lights..or in trafic generaly..) i have to to put it in Neutral so i rev it up and the engine dont dies...
What i checked till now....is the TPS, the knock sensor, the other litle barel near the tps....i checked for presure leaks...(excuse my english), and now its time to check the catalyst and fuel filter....
Any thoughs???

I am no mechnic but I would check the ignition system, plugs wires etc. I would also consider the CPS, EGR. Another check would be vacuum leak. Have you cleaned the TB? If not, do it and be sure the AIS is clean. Other considerations might be the MAP and O2. When was the last time you cleaned the PVC system?

After 15 years, anything is suspect. I know, I have one.

Excuse my ignorance...what do u mean by TB ? and AIS ?...by the way i just changed the fuel filet with brand new...and crosschecked the map with one from a friends XJ...
I will check the O2...and what do u mean the pvc? what excactly pvc ?
Thank you !

Did you check for a vacuum leak in the MAP sensor hose? Mine was split and had some popping noises and reving issues.

scout said:

Excuse my ignorance...what do u mean by TB ? and AIS ?...by the way i just changed the fuel filet with brand new...and crosschecked the map with one from a friends XJ...
I will check the O2...and what do u mean the pvc? what excactly pvc ?
Thank you !

Click to expand...

TB = Throttle Body. When dirty, it can cause odd idle characteristics

AIS = Idle Air Stepper (AIS) - it's mounted to the throttle body, and controls the amount of air getting into the engine at idle.

PVC should be PCV (Positive Crankcase Ventilation). On the 4.0, it's actually CCV (CrankCase Ventilation). It allows the valve cover to breathe so it doesn't build up so much pressure that it blows all the seals out.

CCV on the 4.0 consists of two hose assemblies - one runs from the air box to the front of the valve cover, and the other comes off of the valve cover and goes somewhere I can't recall without looking under the hood.

Hope this helps.

Rob

First of all thank you for the explanation !!!
...if the Idle Air Stepper is the one near TPS... is checked and changed with a brand new one.

I will check for CCV (CrankCase Ventilation)...where is it placed???? and i will spray the TB.. with a cleaning spray...... i also heard about EGR from a friend?
what and where is this?

There's a picture of the EGR control selenoid location in here.
http://www.4x4trailhunters.com/article.php?id=16

The actual EGR is below the TB on the outside edge of the intake manifold. Its supossed to allow some exhuast into the intake at higher RPMs and be closed during idle.

Careful spraying cleaner into the throttle body, the sensors are plastic and the cleaners can and will melt them in short order. Pull the throttle body, remove sensors, then clean it, reinstall sensors and put it back on the motor.
The CCV problem is usually in the back of the valve cover, as the engine over it's life gets a build up of sludge in the top of the head it move the flowing oil closer and closer to the CCV tubes which stick down thru the valve cover into the head area. If you pull the valve cover to clean the CCV stuff out have a shop vac handy as well as a plastic scraper, use the shop vac and scraper in tandem to first break loose the crud and vac it up so it does not end up down in the oil pan where it can block the oil pump pickup. As for the small hoses that go to the air box, don't bother cleaning them, just go buy a new set at the dealer...