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Matt
Matt, Mechanical Engineer
Category: Honda
Satisfied Customers: 22172
Experience:  BEng hons Mech engineering, in auto industry 22 years
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The car cuts at at low speed when it heats up. Once cool the

Customer Question

The car cuts at at low speed when it heats up. Once cool the car operates normally, Heavy, slow moving traffic is a nightmare.
Submitted: 22 days ago.
Category: Honda
Expert:  Matt replied 21 days ago.

Hello
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 or brake cleaner 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 flattened piece 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.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion ill make a leak worse) so leaks can be better or worse as the engine heats up.
1 vacuum leak path that you won't find with the above test is if the brake servo is leaking

so try clamping off servo hose to see if this has any effect

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.

if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

Expert:  Matt replied 18 days ago.

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Customer: replied 18 days ago.
I have to give it to my mechanic early tomorrow. I'm sure all will be fine though. I'll let you know asap.
Expert:  Matt replied 18 days ago.

understood

Expert:  Matt replied 11 days ago.

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Customer: replied 11 days ago.
H,I booked my car into my local garage and gave them your prognosis sheet. I'm afraid it didn't work and no air leaks were found. I've decided to change the car as I cannot afford to break down.
Sorry,