Rough idle smoothes out when warmed up

[blue44]

ok. My 2000 all of a sudden idles rough when cold, smoothes out when it warms up. Toyota scanned and showed random misfires on 1,3 and 4. They suggested I bought some bad gas that may have water in it. I added a can of sea foam and filled w quality gas. CELs immediately turned off. Next day, same rough idle at start up, then smoothes out 10 miles later. I’m on day 4 of this and it’s driving me nuts. I figured I’d turn to the more seasoned and committed crowd for advice/answers. I know the coils can be the culprit of a rough running motor, but I tend to rule them out, since it smoothes out everyday after 10 miles. This cruiser has been babied and has 147,000 miles w all recommended maintenance done......

 

[FxFormat]

My buddy just had this issue, rough idle on startup, car shakes, scanner showed misfire on 3 cylinders, i replaced all 8 coilpacks for him with Densos and it's been fine ever since.

 

[Spike555]

It's not the fuel, any water in the fuel will be removed with the fuel because all of our fuels have ethanol in them and water sticks to ethanol.

Engines need to run rich when cold, so the ECU dumps more fuel into the engine than is actually needed until it warms up, think of it as full choke when cold.
To much fuel and weak spark will cause rough running because the engine is basically being flooded.
Once warm, the fuel mixture leans out and all is well.

Start with spark plugs. That is the cheapest and easiest place to start. 98% odds that fixes your issue.

 

[jerryb]

I'd take odds on the maf and coolant temp sensor.

 

[diego355]

I would start with the easiest and cheapest option, clean your MAF sensor and throttle body.
Very often overlooked

 

[Rolocado]

Disconnect battery for 10-15 mins, clean MAF and Throttle body. Goes without saying air filter too

 

[blue44]

This is all solid advice. I do appreciate the help fellas! I picked up some MAF cleaner today and will clean it this weekend. Then I'll address the spark plugs. I'll update, per my findings. Thanks again for the support

 

[Spike555]

This is all solid advice. I do appreciate the help fellas! I picked up some MAF cleaner today and will clean it this weekend. Then I'll address the spark plugs. I'll update, per my findings. Thanks again for the support

Clean the MAF, won't change anything but a good idea anyway.
Do not unhook the battery, this will just make your engine run weird until it re-learns a drive cycle, which can take a week to do.
Cleaning the throttle body is a good idea, do this before the new plugs are installed and make sure you start the engine after cleaning to burn out all of the carb cleaner.

Please please report back your results so others with similar problems can search, find your thread and find a solution.

 

[blue44]

Spike555, I cleaned the MAF, even though it looked shiny on both sides. It still runs rough for 10-15 minutes, then like it should. CELs still on. Bought a Bluedriver. It tells me misfires on 1 and 3. I plan to buy a set of plugs in the morning and 2 coils. Looks like #7 will be a little tricky to replace. I assume, from what I’ve read, that I should go w Denzo plugs as well. Any advice there?

 

[Spike555]

Of course cleaning the MAF made no difference, your plugs are bad.
A dirty MAF effects MPG not the way it runs. The MAF is what tells the computer what kind of air is coming into the engine. Density, humidity and how much air the engine is getting.
But when cold, no mater what, the engine runs "full choke" until it warms up and the fuel trim is leaned out.
O2's make no difference when stone cold, MAF...nothing until warm. It must run rich until warm. Weak spark equals rough running and random misfires.
It it happend all the time then I'd say coils too. But it's only when cold.

I used NGK plugs. Iridium lasts longer. But you can use whatever you want. I am a huge fan of E3 spark plugs, I use them in everything. Didn't use them in the Cruiser because they were not in stock and I didn't have time to wait.
But thats what's going in next time. Used them in my wifes van too. And lawn mower, chainsaw...everything. I swear but them.

All are easy, just move things to get to them. Takes like an hour start to finish. Removing the resonator air box is the hardest part. There are hidden bolts and some will be rusted. And some of the vacuum lines will be stuck on, just twist and pull to get them loose. Maybe use some WD-40 or the like.

 

[2001LC]

Misfire is often associated with a bad coil, which tend to be worst when hot and under load. Misfire also can be from a bad spark plug(s). Worth noteing; Loose spark plug(s) will tighten (expand) as engine heats, running poor when cold better when hot.

Vacuum lines should also be inspected. Like MAF, vacuum leaks are not direct cause of misfire, but contributing factor that may foul plugs. Fouled plugs draw more current from coil(s) leading to coil overheating and failure.

FSM recommends disconnecting battery before MAF sensor, reconnecting afterwords. Disconnecting battery for 20 minutes reset ECM. Doing this during a tune up, then ECM re-learns with the now tuned engine output (a good thing). This key to getting good results after tune up.

 

[blue44]

Of course cleaning the MAF made no difference, your plugs are bad.
A dirty MAF effects MPG not the way it runs. The MAF is what tells the computer what kind of air is coming into the engine. Density, humidity and how much air the engine is getting.
But when cold, no mater what, the engine runs "full choke" until it warms up and the fuel trim is leaned out.
O2's make no difference when stone cold, MAF...nothing until warm. It must run rich until warm. Weak spark equals rough running and random misfires.
It it happend all the time then I'd say coils too. But it's only when cold.

I used NGK plugs. Iridium lasts longer. But you can use whatever you want. I am a huge fan of E3 spark plugs, I use them in everything. Didn't use them in the Cruiser because they were not in stock and I didn't have time to wait.
But thats what's going in next time. Used them in my wifes van too. And lawn mower, chainsaw...everything. I swear but them.

All are easy, just move things to get to them. Takes like an hour start to finish. Removing the resonator air box is the hardest part. There are hidden bolts and some will be rusted. And some of the vacuum lines will be stuck on, just twist and pull to get them loose. Maybe use some WD-40 or the like.

 

[blue44]

Thanks for the support. I'll be replacing the plugs in the morning and see what that does. I will go ahead and purchase 2 coils to have on hand, if they are still needed. If not, I'll have backups on hand for use when coils die. I certainly appreciate the time and effort you guys are giving this old cruiserhead.

 

[blue44]

Misfire is often associated with a bad coil, which tend to be worst when hot and under load. Misfire also can be from a bad spark plug(s). Worth noteing; Loose spark plug(s) will tighten (expand) as engine heats, running poor when cold better when hot.

Vacuum lines should also be inspected. Like MAF, vacuum leaks are not direct cause of misfire, but contributing factor that may foul plugs. Fouled plugs draw more current from coil(s) leading to coil overheating and failure.

FSM recommends disconnecting battery before MAF sensor, reconnecting afterwords. Disconnecting battery for 20 minutes reset ECM. Doing this during a tune up and ECM re-learns with the now tuned engine output (a good thing). This key to getting good results after tune up.

 

[blue44]

I will check the tightness of the plugs, as I remove them, especially #1 and 4. That's good advice too. You guys rock. Lots of knowledge to be shared and learned on this forum. I appreciate everyone's willingness to help!

 

[blue44]

Ok. I replaced all plugs. #7 was a MFer. Scanned for codes. Only had one code stating misfire. This was good news. I replaced coil w Denzol on the coded cylinder. Cranked, felt smooth, cleared my CELs, scanned the truck again and found zero issues. I'm a happy camper. I did go ahead and clean the throttle body, since it was right there exposed. It had a black film, but no heavy carbon buildup was felt or seen. Thanks again for all the support fellas. Toss you a beer if I ever see you. FWIW, a Trollhole advised me to purchase a Blue Driver code reader. It was nice to use it while I stumbled my through my repair. Thanks again for your time and energy to help a fool out!

 

[Spike555]

You're welcome.
Thank you for reporting back.