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Matt
Matt, Engineer
Category: Car
Satisfied Customers: 21372
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Isuzu Rodeo: I have a 1997 Isuzu Rodeo S (4 cylinder) that

Customer Question

I have a 1997 Isuzu Rodeo S (4 cylinder) that I just bought from a friend. It has all the symptoms of a vacuum leak (runs great when cold and then starts to stutter while driving and stalls when idling). How do I find the vacuum leak?
Submitted: 1 year ago.
Category: Car
Customer: replied 1 year ago.
The "check engine" light is on. My friend, the previous owner, said it came on alot while he drove it, especially when he went over bumps...and then it would go away. He thinks there is a short somewhere. But when I had the guys at Autozone plug their device into the car, two codes came up...P1406 and P0041. Maybe this info will help
Customer: replied 1 year ago.
By stutter, I mean it feels like it is misfiring while driving. Also, I am not sure but sometimes I think I smell some gas fumes when I exit the vehicle after driving it. Is it bad for me to continue driving it in this condition? Will I damage anything? I have to get to work while I try and fix it myself or pay someone else to do it.
Customer: replied 1 year ago.
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Expert:  Matt replied 1 year ago.
Hello I'd agree that 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.however the code P1406 is a EGR fault which can also give issues and the 0041 code is a oxygen sensor fault so both of these should probably be investigated 1stcheck the connections to the EGR valve, if either the vacuum pipe of electrical connection are damaged / corroded then the EGR can be on all time which certainly will hurt performance. Its also possible that its a fault with the EGR valve so its worth removing the valve and cleaning it out with brake cleaner, if it looks particularly clogged then replace it. 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 if this is OK then consider replacing the sensor and finally to detect a vacuum / air leak 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. It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine Might also be worth cleaning out the idle speed control motor / valve as these get clogged up with carbon and some brake cleaner washed through helps free things off. Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.if the engine condition is the same then chances are the meter or the connection to it is faultyAir leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them. This leads them to be quite intermittent in the case of mild leaksits also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue On no account touch the sensor wires with anything physical as they are extremely fragile