Cold Start - Low/Rough Idle and Bucking

[Anthony17]

Hey all,
So I've been doing a ton of reading on the issue I've been having, and haven't really found the solution yet. I have a 2000 EX EB 4.0 SOHC with 230,000 miles with rebuilt transmission. Was very well maintained. On cold starts only (1st start of the day), my truck has a really low idle. It bounces between 300-500 rpm, and bucks/shakes, the interior lights/dash lights flicker to the shaking because of the low rpm. After about 10-20 seconds (depending on how long it sits) it will shoot up to 1500 rpm and settle back down to idle. Then it is fine for the rest of the day. I'm worried when the winter comes that this issue will be worse.

When I try to give it a little bit of gas, it revs up to 1500-2000 rpm and I can't seem to give it just a little gas. To me, this sounds like a vacuum leak. It seems the supposedly bad gaskets need to get warm and expand on initial start of the day, then the warm summer days do the rest of the work. It's been in the 60's in the mornings so far. I have only had it since June of this year, so no winter weather with it yet.

On to what I've replaced or fixed related to engine components:

• New IAC valve

• Spark plugs and wires

• ECT sensor

• Thermostat

• Air filter

• Oil filter and oil change

• Fuel filter

• Cleaned throttle body

I tried to replace all the common problem components (as it's old with many miles and I don't know when these parts, if ever, have been replaced) before I came to ask more questions. I also ran sea-foam through a tank of gas.

Right now I am currently waiting on a new downstream O2 sensor (to fix current CEL), IAC gasket and upper/lower manifold gaskets. Could either of these be my potential fix? Maybe it's the ignition coils? I know those manifold gaskets are also a common issue for rough idles, but I'm not sure if it attributes to my exact issue. Any ideas? Am I going in the right direction?

 

[chefduane]

Have you checked to see if it is throwing any codes?

 

[Anthony17]

Yes, it's only throwing the P0036 B1S2 heater malfunction code. I have scan software I use and it doesn't see any other issues. That's what my new O2 sensor is going to fix, and since it's downstream it wouldn't be related to this issue. All four O2 sensors were replaced in 2012 according to some receipts I found in the glove box.

 

[Anthony17]

Bump - Any thoughts??

 

[JusTheUsual]

Could be antifreeze leaking into cylinder(s) due to bad head gasket.

 

[Anthony17]

Never heard of that. Would I be able to confirm that with the upper and lower intake manifolds off? Or how could I?

 

[Explodr94]

Sometimes you have to reset computer when replacing the IAC.

 

[funfool]

It bounces between 300-500 rpm, and bucks/shakes, the interior lights/dash lights flicker to the shaking because of the low rpm. After about 10-20 seconds (depending on how long it sits) it will shoot up to 1500 rpm and settle back down to idle. Then it is fine for the rest of the day.

I just wanted to add, I have the exact same symptoms with my 98 4.0
I have only owned it for a few weeks, it really is a minor issue at this point.
Let it run on its own and it is between 500 rpm and about to die, then over corrects and jumps to 1500.
But if you stick it in gear and drive it 30 feet, it is all back to normal.
And only the first start of the day.

I would find it hard to believe that it has a bad head gasket, but have been wrong before.
It simply runs to good and the temp gage stays right in the middle, no white smoke etc etc ...
Just wanted to add that I was watching this thread because have the same issue, and was getting ready to throw the parts cannon at it.
Anthony has been kind enough to tell me what not to throw at the problem

 

[Anthony17]

I'm glad someone else is seeing the same issue and I'm not going crazy. I've let it be many mornings and just let it do it's thing, but I'm worried it's going to get worse when it gets colder out. It will be my winter beast mainly. I get no white smoke, milky oil, or bubbles in the radiator, so I believe it's not coolant leaking into the cylinders (which those are the symptoms). This symptom just seems too odd and specific. I will report if it changes after the manifold gasket change I'm going to do.

 

[funfool]

Please let us know what you find.
I cant do much with mine right now, am doing some needed bodywork to it.
Actually made a thread on it here http://www.explorerforum.com/forums/showthread.php?t=432244

And being disabled, I can work on it for a few hours, then need a 2 day rest.
And money is a little funny right now, not being able to work for over a year, and fighting social security disability.

But if there are some things I can try and experiment on, certainly would.
I dont have a cel on, I do have a cheap code reader and can hook it up and see if any stored codes.

I have been reading of the lower intake gasket leaks and idle, but it really does not fit our situation.
Yesterday I started it right up and waited 5 seconds and put it in gear and started driving it. You can feel it chugging along and literally 15 or 20 feet, you can feel it fix itself.
Just like turning a light switch, the idle becomes stable and solid power.
It will take over a minute to sit in the driveway warming up, for it to correct itself and get normal idle.

My odometer shows 198k. But I dont know if it is a original engine.
I believe it was well taken care of, before the accident, it has new axles in the front and also the front differential looks new, compared to all the dirt around it on other parts.
The motor just runs sweet, is no valve or timing chain noise.
Only noise is from the fan pushing the air.
Also the motor has no oil leaks, it has road dust but not dirty, it has a sticker on the valve cover that gives the engine specs, and has a sku number.
Every hose clamp on this thing is brand new, I just think it has a rebuilt motor installed and no idea the mileage.

So at what mileage does the lower intake gasket kick in to play?
Just a guessing game at what mileage the original motor cut loose at. If it was 120k, then my rebuilt has 80k on it. You would like to think they got 150k on the original motor, then I have 50k on the rebuilt.

Just pointing out, I dont think it is a mechanical malfunction with the engine, more a electrical or sensor issue. The way I can put it in gear and drive it a few feet, and feel something kick on and the problem is gone.

Can you confirm that if you drive yours for a few feet it goes away?
I prefer to let a car sit and warm up, just seems like the pcm is getting one set of instructions, but when put in gear it changes instructions and corrects itself.
Now I have to try that ... put it in gear without moving, see if it corrects itself

 

[funfool]

I checked for codes, my cheap scanner just searched and said no codes stored.
So I made a youtube vid of it here.
https://www.youtube.com/watch?v=702hKTyYGuY&feature=youtu.be

It does not last long, it is just about finished at 1 min when I get out of the car to listen to the exhaust.

 

[Anthony17]

Just an update, I replaced my upper and lower intake manifold gaskets. The lower ones were definitely shot and the upper ones weren't far behind. I zipped it all back together tonight and started her up. She had a tough time at first crank because it was sitting for over a week and I had the battery/Pam disconnected for a couple days. That initial start I expect to take longer because of the new gaskets. But after it settled in, I manually raised the idle just a tad, as it tried to settle in a little above 500 which just shook the truck too much for my taste. She has a lot of miles so I don't feel bad raising the idle a little higher. But it did seem to respond better and idle smoother. I guess time will tell over the next day or two when I can test a cold start. I will report in with the results soon!