1998 avalon misfire when cold - Toyota Nation Forum : Toyota Car and Truck Forums

whackerstick · 01-31-2011, 08:52 PM

My 1998 avalon has started jumping, surging, misfiring,and in general running ragged, especially when cold. After it reaches normal temperature it straightens out somewhat, but not completely. I cleaned the throttle body, put in a new air filter, tested the tps,pulled the front bank spark plugs ,they look fine. I tested the coils with a digital ohm meter,one of them read just a shade different (10.25k ohms while the other two read 9.85k ohms).It hasn't put out any trouble codes or lit up the check engine light. Anyone have any suggestions? My wife is giving me grief ,please help

***TrailDust*** · 02-01-2011, 11:09 AM

Have you checked for coolant loss? One possible cause is if you have a coolant leak into one or more of the cylinders it'll coat the spark plugs and cause the kind of cold start misfires you're describing. I'd start with that.

pmesfun · 02-01-2011, 12:47 PM

Also, check the resistance and clean the IAC Valve.

Jack Deth · 02-02-2011, 06:36 PM

water in your gas?

whackerstick · 02-02-2011, 09:29 PM

Don't think water is in gas,just filled up with super unleaded. It was doing this before . I did some more testing, and noticed when idling if I jab the throttle sharply it will spit back and you can hear it in the exhaust,but if you ease down on the throttle it doesn't, but when you drive down the road and punch it ,it surges and doesn,t accelerate as it should.
Could it be a bad coil pack? The plugs have about 40,000 miles on them, maybe they are missing.Do the wires give much trouble? What sensors could be defective and not throw a check engine light?

tacosteelersman · 02-03-2011, 08:58 AM

MAF (mass air flow) sensor could be dirty, they sell MAF cleaner.

***TrailDust*** · 02-03-2011, 05:13 PM

Quote:

Originally Posted by whackerstick

Don't think water is in gas,just filled up with super unleaded. It was doing this before . I did some more testing, and noticed when idling if I jab the throttle sharply it will spit back and you can hear it in the exhaust,but if you ease down on the throttle it doesn't, but when you drive down the road and punch it ,it surges and doesn,t accelerate as it should.
Could it be a bad coil pack? The plugs have about 40,000 miles on them, maybe they are missing.Do the wires give much trouble? What sensors could be defective and not throw a check engine light?

But did you check the radiator/coolant level?

whackerstick · 02-03-2011, 08:22 PM

The radiator is full. I removed the maf ,bought some crc mass air flow cleaner and cleaned it. I will put it back in the car tomorrow, and try it. Is there a way to test the maf with an ohm meter?

pmesfun · 02-03-2011, 08:37 PM

Yes, here is the procedure.

whackerstick · 02-08-2011, 04:30 AM

I got a new coil pack and replaced each one , and as usual it was the last one I swapped that cleared up the misfiring when cold. The car runs a lot better now ,but it still shutters on hard acceleration from a stop .If you feather the throttle it seems to do ok. After you reach normal driving speed and accelerate heavily or hit passing gear it surges. I do notice the temperature of the car doesn't reach up to halfway like it used to ,it only reaches a little over a 1/4 ; possibly a thermostat stuck open? I plan to change it when I get time. The maf sensor tested ok.

***BMR*** · 02-08-2011, 02:01 PM

Quote:

Originally Posted by whackerstick

I do notice the temperature of the car doesn't reach up to halfway like it used to ,it only reaches a little over a 1/4 ; possibly a thermostat stuck open? I plan to change it when I get time.

Yep, most likely the thermostat is opening too quickly. That's a common failure mode for them. Word of advice on a replacement: DO NOT use anything except a genuine Toyota thermostat. They are well worth the extra few dollars. In the case of thermostats, most of the aftermarket brands out there are crap!

whackerstick · 02-09-2011, 07:57 PM

Anyone have a video on changing out the thermostat?
Is it much trouble?
I noticed that my car has a red colored antifreeze, I'm used to seeing a green colored antifreeze. Is it necessary to put the same kind back in the car?

pmesfun · 02-09-2011, 08:16 PM

Quote:

Originally Posted by whackerstick

Anyone have a video on changing out the thermostat?
Is it much trouble?
I noticed that my car has a red colored antifreeze, I'm used to seeing a green colored antifreeze. Is it necessary to put the same kind back in the car?

It isn't that difficult if you have the tools. I changed mine out a couple months ago, only trouble was getting the large engine harness out of the way.

Yes, you need to refill with Toyota Red Long Life Coolant, costs $18-24, but you essentially getting 2 gallons as it comes concentrated. Make sure you mix with Distilled Water. Also, use Toyota thermostat.

whackerstick · 02-14-2011, 03:23 PM

I changed the thermostat,and and the temp. now is normal.Also put in a new fuel filter. The car still backfires on acceleration, and surges on light acceleration.
I let the car idle, and disconnected the wires to the back bank one at a time, the one on the new coil will arc a good 2 inches , the other two about 3/4 of an inch , maybe these are the problem. I ordered 2 more coil packs to see what happens.
Is there any way there could be a fuel pump problem? Still no check engine light.

whackerstick · 02-17-2011, 04:54 AM

I appreciate all those who had input on my problem, but I finally figured it out. I had a weak coil pack that would misfire under load. This was a rather annoying trouble. The part that got me was the check engine light not coming on, but I guess man is sometimes smarter than machine. Again thanks to all.