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Matt, Engineer
Category: Kia
Satisfied Customers: 21599
Experience:  Mechanical Engineer BEng Hons22 years experience in car engine industry, 10 years in formula 1
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I have a 2004 amanti, and the idle is rough. It stays pretty

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I have a 2004 amanti, and the idle is rough. It stays pretty consistent around 750 ram, just very rough.
JA: Is the rough idle intermittent or consistent?
Customer: Consistent
JA: Are you fixing your Amanti yourself? What have you tried so far?
Customer: Yes I am. I have changed pcv valve, replaced vacuum lines, plugs, wires and coils, taken off the throttle body and cleaned.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I can't think of any thing


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.

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 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

Customer: replied 7 months ago.
When idling it does not go up but down. It idles at about 750, but drops down to about 550.


I'd still do the check for air /vac leaks as the next step

Customer: replied 7 months ago.
Could there be a vacuum leak inside the valve cover?


its possible

as the inlet manifold is linked to the cover via a 1 way valve

if you remove the oil filler cap and the idle speed increases then this points to this valve being faulty

Customer: replied 7 months ago.
I'm waiting for the new valve covers to get here.


Customer: replied 7 months ago.
I've checked all the vacuum lines, made sure the egr solenoid was working, checked the tps and the idle air control valve, and changed the valve covers and pcv valve. Still idles low and a bit rough.


in that case I'd next remove the air inlet pipe and clean out the throttle body with a lint free rag and some brake cleaner

and also do a compression test across all cylinders as they should all be within 10-15psi of each other

and 1 low cylinder will also give this kind of result

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