Rough starting intermittently - Toyota Nation Forum : Toyota Car and Truck Forums

AAA99Corolla · 10-24-2011, 12:05 AM

99 Corolla CE

Intermittently I will have a hard start and a rough initial idle that smooths out as the engine warms up. This seems to happen more when its wet outside.

So I changed the Spark plugs, spark plug wires, 2 new ignition coils, air filter, and fuel pump. The problem is still there though...any ideas what it could be?

I read in another post that the MAP sensor could be culprit. If so, does anyone have the OEM expected resistance of the sensor?

Highway_maniac · 10-24-2011, 04:22 AM

Please describe the rough idle. Are the rpm's too low, to high, or is the car hunting for the right rpm (revving / almost dying/ revving it up again).

Map sensor may be a culprit, but it is also possible that your throttle body is dirty. There is an idle control valve on the throttle body, if it is sticking the rpm's may suffer. The idle valve has to open more when the engine is cold, thus the problem may not be noticable when the engine is hot.

Other possiliblity is a air leak in the intake / outlet system. You can spray something flammable (think brake cleaner will work) on the intake while the engine is running (and is cold). Use carefully, spraying only a litte at a time. If the rpm's or sound of the enige change, the engine may get some false air. When the engine heats up, the metal expands thus closing the hole / gap.

Outlet system I don't know how to check, heard about a smoke test but don't have any experience with this.

Good luck in hunting down the problem, and let us know the sollution.

AAA99Corolla · 10-24-2011, 08:12 AM

I think I'll go ahead and change both of those. What are the OEM manufacturers of the MAP sensor and IAC valve?

Highway_maniac · 10-24-2011, 08:39 AM

You can clean the IAC valve before replacing it. Don't know the part numbers / manufacturers, but know they can be expensive.

landphil · 10-24-2011, 06:29 PM

Sounds like a good time to do a compression test, as a weak cylinder could give those symptoms as well.

leakyseals · 10-25-2011, 08:49 AM

A intermittent rough start means to me its choking on something in the combustion chamber or the engine is lacking proper lubrication.

Are the rough starts on cold days or days the car sits longer? Have somebody start the car in morning while you watch the exhaust. What do you see?

What is the oil consumption? What weight oil are you using? Look inside the filler hole. Clean or dirty?

Symptoms for a dirty IAC are usually consistent - wont high idle at startup, idles down too fast before the car is warm, idles too low when the car is warm, slow fluctuating/hunting idle.

AAA99Corolla · 12-07-2011, 12:32 AM

So I cleaned the MAP sensor and reinstalled it. The car has been running fine for approximately 4 weeks now.

But, today I filled up at the gas station.
While driving the engine will suddenly shut off and I'll coast along until the car comes to a stop. It seems like an electrical problem of some sort. The funny thing is, no CEL at all while the engine dies unless I throw the trans into neutral (auto). The CEL, Battery, and Oil lights all go on.

Any diagnostic advice would be helpful. Thanks for replying guys...

Right now I am using 5W30 and it was just recently changed when I cleaned the MAP sensor. The level was fine when the engine started dying out on me.

Any chance that this could also be a case of bad gas?? I filled up at a Speedway 87 octane...my fuel pump is new btw.