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This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.
Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Ok in that case try a check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.
The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers
I'd also check the condition of the engine ground connections, these all have to be tight and clean
the main battery one is obviously important but also check the small wires that run out of the wiring loom and are secured to the engine with ring terminals
also when you have the monitor running how does the ECT and IAT readings look?
steady and stable ?
As if not then its possible a duff signal form either of these could make the engine hesitate
Ok I'd next try pulling the distributor cap off the engine and inspect it for cracks and damage, do the same for the rotor arm
I don't think that the timing is adjustable on the distributor body but yo ucan check it
At the diagnostic connector under the hood, install a jumper wire between the TE1 and the E1 terminals. Restart the engine and check the base timing. It should be 3 to 7° BTDC. Remove the jumper wire and check the controlled timing. It should move between 7°-18° BTDC.
if its moving more than this then is a sign of loose timing chain.
not that then
is the carbon brush in the distributor cap in good condition ?
in that case I'd suggest doing a compression test on all cylinders to confirm that the engine health is good, as they should all be within 10-15 psi of each other
Ok I'm going to opt out and get another expert involved, whom hopefully has direct expierence with this issue
Hello, I have read all the questions and comments posted on this thread and all the things that were tried already but there are two things I see that might be the problem, if you've already tried this please disregard them but it's all I have for you:
try cleaning the throttle body, get all the carbon deposits out and make sure the gasket is in plsce
the expert that opted out may have been on to something about the ECT sensor, it's located at the end of the cylinder head near the firewall. good luck and please let me know if this helped at all, thanks.
thanks for the reply, it's possible the it has a bad ECM.
Thanks for the reply but I don't have any other ways to go on this except that maybe there is a wiring harness problem between the engine sensors and the ECM.