Map sensor query
Discussion
Hi all.
Since resetting my adaptive maps, my car hunts a lot on idle. I've tried adjusting the idle and performing the tps reset but no joy.
Whilst working in the engine bay with the ignition on, when I open and close the throttle, the map sensos makes a very loud clicking noise. Would anybody be kind enough to pop there clam with the ignition on (not running but ignition lit up), open the throttle and report back about any noises?
Massive thank you in advance!
Since resetting my adaptive maps, my car hunts a lot on idle. I've tried adjusting the idle and performing the tps reset but no joy.
Whilst working in the engine bay with the ignition on, when I open and close the throttle, the map sensos makes a very loud clicking noise. Would anybody be kind enough to pop there clam with the ignition on (not running but ignition lit up), open the throttle and report back about any noises?
Massive thank you in advance!
The boost control valve is pulse width modulated at around 15Hz, this is to vary the amount of plenum pressure fed to the boost control capsule, that uses this pressure to push open the exhaust turbine bypass valve (wastegate).
When you move the throttle, the boost pressure "target" calculated by the ecu changes (because more throttle = more boost) and when the engine is off, the plenum is sat at atmospheric pressure. Hence at some throttle angle where the target exceeds the actual plenum pressure, the boost control system will attempt to increase boost by changing the value of the pwm signal sent to the control valve.
Of course, normally, with the engine running, the noise of the engine (and the screams of your passengers... ;-) masks that noise. Most road car ecus suspend this action when the engine isn't running, but the more, er, aftermarket ones don't bother, and hence you can hear it doing it when KOEO!
When you move the throttle, the boost pressure "target" calculated by the ecu changes (because more throttle = more boost) and when the engine is off, the plenum is sat at atmospheric pressure. Hence at some throttle angle where the target exceeds the actual plenum pressure, the boost control system will attempt to increase boost by changing the value of the pwm signal sent to the control valve.
Of course, normally, with the engine running, the noise of the engine (and the screams of your passengers... ;-) masks that noise. Most road car ecus suspend this action when the engine isn't running, but the more, er, aftermarket ones don't bother, and hence you can hear it doing it when KOEO!
I'm fairly sure it's the map sensor. It can't be a sealed unit can it, air passes through it?? Take it off the manifold and blast electrical contact cleaner down the opening (manifold side). Do not use WD40 or anything similar only use proper contact cleaner. There is also a sensor on the inside of the throttle body but I think it's just a temp sensor not a maf sensor but worth cleaning it while you have the cleaner out.
It has a vacuum port on one side only. Effectively it's a vacuum operated variable resistor. Doesn't actually directly connect to the inlet manifold, just bolts to it. Will clean what I can anyway 
Out of interest, does anybody know what the correct inlet manifold vac pressure is or should be on idle? Lots of different opinions with turbocharged engines!
Thanks
Out of interest, does anybody know what the correct inlet manifold vac pressure is or should be on idle? Lots of different opinions with turbocharged engines!
Thanks
Why check at idle?
It should be "atmospheric" pressure without the engine running!!
tbh, you are more likely to damage the MAP sensor trying to clean it. I've never known one to be dirty, so as long as it reads the correct pressure with the engine off, its almost certainly fine!
(BTW typical MAP at idle will be around 30kPa(abs). But it depends on numerous factors which are all very variable)
It should be "atmospheric" pressure without the engine running!!
tbh, you are more likely to damage the MAP sensor trying to clean it. I've never known one to be dirty, so as long as it reads the correct pressure with the engine off, its almost certainly fine!
(BTW typical MAP at idle will be around 30kPa(abs). But it depends on numerous factors which are all very variable)
Not really.
If you have a pre throttle air leak, you won't find it at idle (in fact, you'll struggle to find it at all)
If you have a post throttle air leak, chances are your engine will struggle to maintain it's normal idle speed, and you can usually hear the leak too. You can also find leaks at idle with a tin of spray carb cleaner. Spray where you think the leak is, and the engine speed should change as the mixture changes as the carb cleaner gets sucked into the engine.
If you have a pre throttle air leak, you won't find it at idle (in fact, you'll struggle to find it at all)
If you have a post throttle air leak, chances are your engine will struggle to maintain it's normal idle speed, and you can usually hear the leak too. You can also find leaks at idle with a tin of spray carb cleaner. Spray where you think the leak is, and the engine speed should change as the mixture changes as the carb cleaner gets sucked into the engine.
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