Hi , I was out in the car last night when it suddenly developed a misfire , so today i pulled the plugs and gave them a good clean as well a the dist cap , replaced and still no difference .I have had a issue with an uneven idle for a while , would the idle control valve cause this to appear , the car starts fine runs rough but will idle ,although a bit rough , it will not stall . I’m not getting any error codes either .I have a spare Idle control i took off a parts car years ago and cleaned up . I also have a fear of maybe a dropped or burnt valve (all sorts of bad things running through my head ) .would signs of that be noise and smoke ? it is not smoky at all . I have also thought of maybe fuel contamination , i did put fuel from a station i don’t normally go to. any and all thought appreciated .thanks Mark
After thought , would topping the tank off with a higher octane fuel be of any use ? Mark
Mark I have a 1987 3.6 xj40 with 124k here in New Brunswick. I had the exact same problem after purchasing the car which had been in a moderate front end accident. I fixed mostly everything and the car ran ok except for that very same rough idle you’ve mentioned. My mind raced also mostly with really bad stuff!! So I took control of my thoughts and imagination and started slowly looking for clues. My first thought was a small vacuum leak as I could hear the tell tale “hiss”. Yip I found it but darn, it wasn’t the problem. I was discouraged but kept looking. Checked and cleaned the plugs, distributor, rotor, wires etc. Nope. I even checked the “slack” in the timing chain thinking that the timing chain was stretched or the guides warn. Absolutely no slack. For a joke I decided to stick a screwdriver to each fuel injector to listen for the pattern of ticking. Sure enough, one of the injectors, actually the second from the front was not “ticking”. I tapped on it a half dozen times and would you believe the injector came to life and the idle smoothed out just beautifully. Your description sounds so much like what my problem was. Give it a try.
Check it out and let us know. I have other possibilities it could be. Good luck. Peter
Thanks Peter , will give the high tech fix a go in the morning , belting down with rain atm , only have a carport .
had a break in rain , high tech screw driver handle didn’t work .put some injector cleaner in tank will run the car for a bit tomorrow.
Try unplugging and cleaning/tightening the terminals of all the sensors on the LH side of the engine, Coolant, MAF, and air temp etc.
One more thing about the injectors. What I did was unplug each injector one at a time with the car running. The car ran horribly rough with the disconnecting of each injector except for that second one. The car ran exactly the same with that injector plugged or unplugged (mildly rough) and made no difference at all. That’s when I tapped on the injector and it revived and solved the problem!
Something I checked too was the intake manifold bolts. I tightened them each a quarter turn in case they had loosened/stretched over time and we had a small leak there. Wouldn’t hurt to remove and give your throttle body a complete cleaning. Mine was spotless but it was worth the check. I’m still leaning towards dirty injectors or a small vacuum leak. Good luck Mark.
thanks Larry will give them a try , can’t hurt. at the very least they will all be clean , what would i use for the MAF as carb and throttle body cleaner are not good for it i’ve heard.
Thanks Peter , i’ll try that before i start to take it all apart.
You can get MAF cleaner, but all I would clean and tighten would be the MAF electrical connector along with all the other sensor connectors
early in the morning here when i read and misinterpreted the meaning , coffee has cut in now and am a little sharper , lol .
had a bad rainy day today , managed to clean the spare set of injectors i have , got in the car to run it to try and run the fuel down (added injector cleaner) carport flooded , ran it for about 45 mins . suddenly there is a “fuel failure” on the dash . OK , now i have something to chase , hoping tomorrow is abetter day , will keep posted.
Try 98 octane, had the same problem with mine when running 91 octane
If you’ve unplugged/cleaned all your sensors it could be that one of them is not contacting
at the pins perfectly. I’d disconnect the battery to dump the codes, make sure your sensors are all connected and retry. Just a thought.
Hmmm … there seems to be a bit of a misconception on what the octane level in gasoline means.
def: Octane … a colorless flammable hydrocarbon of the alkane series, obtained in petroleum refining.
Most people think that higher octane in gasoline “supercharges” the combustion in an engine cylinder, giving them additional power, performance and more torque. This is simply not true.
The octane rating of gasoline essentially tells you how much the air-fuel mixture can be compressed before it will spontaneously ignite. The greater the octane level the less likely the air-fuel mixture drawn into your cylinder will pre-ignite or PING under high pressure (read full acceleration) when the maximum amount of air and fuel is being introduced.
In other words you don’t want the fuel air mixture igniting BEFORE the spark plug fires,
lower octane gasoline is basically the same as higher octane gasoline EXCEPT for the octane level.
Mark. I assume that you have change your fuel pump because your car is an 89, If not the pump can flutter because of the very high temps we have being getting in Ontario and that will cause a problem similar to your discription
had the car for last 18 mths , don’t know how old fuel pump is , been no problem as far as i know . weather here in australia is cold atm .
Larry , when saying air temp sensor do you mean the sensor to the catalytic converter on the exhaust or some other one , if the last one , where is that located . i’m not too savvy when it come to electrical stuff.
When I saw markON I though you lived in Ontario Canada.The fuel pumps in the 89 fail sooner than later.Its not in the gas tank,so check it out left side of car in rear wheel area
easy mistake , OK thanks