1999 Corolla engine runs rough and rattles on idle.?

Question

I have a 1999 Corolla with 160k miles. Each morning, when I first back up the car from the garage, the engine runs rough and it rattles, then it settles down somewhat when I put the gear in park, . When I'm on a stop light and the gear is on D1, the same thing happens - the idle is rough. Engine has been very reliable, never had any problem, except the rattling bothers me and I worry it maybe a prelude to something bad. I'm thinking it may be tension belt(s). But if it's the tension belt(s), why would it make a difference if it's in park or reverse. Also, belt looks okay from visual inspection. I change oil regularly, every 3k to 5k miles. Any help will be greatly appreciated. Thanks.

Answer 1

it could be your IAC (idle air control) valve (if it has one) or your mass air sensor screwing with the idle making it run rough.

Answer 2

Have an OBD2 check done to see if the problem is in the engine or its controls. With the engine cold, remove the serpentine belt and start to engine to see if the noise is absent under that condition. Keep that test very brief, because you will not be operating the a.c. compressor, alternator, power steering or water pump. What it will show is if any of those rotating things are creating the noise. If the rattling persists without the belt on, that eliminates rotating accessories. Don't forget to examine the harmonic balancer (the crank pulley) to make sure its rubber union hasn't separated. It usually takes around 200,000 miles to wear one out, but be thorough. Exhaust pipes and heat shields can break lose and rattle. Look at all the motor mounts. The OBD2 test may indicate something is malfunctioning and will name the part. Replace bad parts. In the garage, with it dark, put a flashlight in the air intake passage and look for light shining though cracks. Replace cracked plastic parts. Do not run the engine in a closed garage.

Answer 3

provide the throttle body and the "IAC valve"( Idle Air administration) a reliable sparkling positioned on suitable of the throttle body. If the placement keeps then seem at spark plugs and HT leads.