Technical Car Experts Answers everything you need: car idle rough and stalls

The engine starts fine but runs rough.

Inspect the fuel which is inside.If its dirty or wrong fuel filled the problem of vehicle running rough can occur. Also get the fuel pressure checked.If the pressure is low then required,then vehicle will run rough.

If the pressure is low,then problem relates to faulty fuel pump and clogged fuel filter.Inspect and replace both,if checked out faulty or very old.

At our repair garage,one customer with same problem of engine running rough,the issue was with the fuel is backing up into your emissions canister causing a rich condition due to too much fuel and trying to flood the engine.
Try not topping off the tank when filling and try filling the gas at a slower rate. If these don't work have the emission system checked for clogged tubes, clogged charcoal canister or a bad vent control valve. You will need a scanner for this or have a dealer or repair shop scan it for you.

On some cases engine light keeps coming on and the car bogs down and runs rough.

On that cases the vehicle engine module needs to be scanned,to retrieve the error codes stored in it.

Also on cases the problem is related to low compression on engine cylinders.
So in that case the low compression cylinder needs to be replaced.

But if compression checked ok,or before directly replacing the faulty low compression cylinder I recommend to inspect valve.On some of such cases the problem was a bad valve causing the problem. There is a simple test to determine if it is a valve or not.
Take a cap full of motor oil and put it into the cylinder, then retest compression. IF the compression is higher, then the problem is with the rings, if it stays the same, then it is a valve issue.
This is a effective test to determine which way to go on the car.

IF in case the Kia Rio runs rough at idle but is OK at higher RPMs

Then check the timing belt to make sure the timing marks still line up and not got misaligned. Other then that check the throttle position sensor (tps).
You can easily test the TPS. For that unplug the tps and with a volt meter set to ohms check the resistance between the top and middle terminal. The reading should be 1.6-2.4 ohms with the throttle closed.

If in case the timing marks are not aligned right,then to realign the timing marks.

You should never turn the cam, you should always turn the engine at the crank shaft.

See the help diagram shown below to realign timing belt marks:----

Please note to align timing marks the Intake and Exhaust cams both have to line up with the two nibs at the top, and the dowel pin on the crankshaft must line up with the pointer above the crankshaft gear.

AT out garage we received same problem,with one of the client.He towed the vehicle to our garage and these is what we did,.

It was timing marks misaligned.

At our auto repair garage store we opened up the timing cover and found that the rear cam was off by one tooth in the counterclockwise direction and that the forward cam was off by two teeth in the clockwise direction.

Always keep the appropriate diagrams handy,these let you know how exactly the timing belt has to be set.

Correcting the situation may be very tricky if you are newbie or doing it first time.But patience is the key, don't panic and go step by step further very gently. It will take you about 3 to 4 attempts before you can finally understand the simple method to do so.

Keep basic auto repair tools handy.You will need to use a ratchet on the cam sprocket bolts to position them and keep them from moving .Always do these task with someone there to help you,to hold the tools or to engage the timing belt with the sprocket teeth. Once these is done now you can start by seating the timing belt on the crankshaft sprocket and using it to line up the marks.

Once these is done then proceed to the rear cam, then the forward cam, and finally installed the tension pulley on the forward side of the engine.

Once these all procedure is done.Now see carefully near you,that nothing is got left out.Close the cover and now test your work,which you have performed.In our garage repair case the vehicle runs like new and customer was very happy.

These details will help.
Thanks.

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PLEASE HELP.
MY CAR IDLES ROUGH AND ALSO STALLS WHILE DRIVING.
MY MECHANIC SAID ITS VACUUM LEAK PROBLEM.
WHERE SHOULD I TRACE VACUUM LEAK.
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OK.

The vacuum leak in or around valve at rear of fuel injector pipe can cause this problem.

This is entirely possible there are numerous places in that area where a vacuum leak can occur, the easiest way to test for vacuum leaks is by using something like Carby cleaner to spray around the area. If the idle quality improves then you have identified the area where the leak is. Just be wary of spraying products like this around very hot engine components.

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THANK YOU.
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