High Rev on Startup, possible fix

[JOEZ33]

I've read through most of the posts involving this random problem the SOHC engine has with a high rev at startup. Just to recap the problem, some owners will suddenly have a new problem where during a cold start (engine not warmed up) the engine starts like you have the accelerator floored, and it screams quickly to 2,000 rpms before oil pressure even shows a reading. This causes some pretty awful noises in the engine, and probably eventual damage.

About 6 months ago I had flashed my computer to a towing mode, from the previous economy mode. Suddenly it was starting with a high rev. After a week of towing, I reflashed the economy tune, and the starting was normal again. This lead me to believe it's completely 100% related to the computer, and not a vacuum leak, or IAC problem, or throttle body problem that has so far all been suspected. People have posted quite a few attempts to clean or change all these parts with absolutely no cure to the problem, they always still have a high rev at startup.

So fast forward to last month, the high rev problem showed up after an oil change, and never went away. I reflashed the computer twice, with no change at all, did not fix the problem.

Yesterday I decided to unhook the battery for the afternoon while I was at work. I reconnected the battery to drive home. When I restarted it, it did a slight rev to 1700, but not too quickly and no loud noises. Today (this morning) I started up, and it didn't even come close to revving high at all! It started completely normal, slowly went to about 1300 rpm, then dropped to 1,000 for a few min while warming up. It actually started quickly without excessive cranking, as in- the second I hit the key it was already running.

I think that quite a few other people have all had the same high rev problem start immediately after their oil was changed. Somehow the computer learns something during that first start with no oil pressure and it stores it for future start ups. This is my belief. Reflashing changes certain parameters, but does not erase everything that is learned during normal driving. (another novice belief). Unhooking the battery lets 100% of the learned variables to be deleted, and gets rid of what was causing the high rev on start up.

So since this problem is quite common on the SOHC engines, and some people don't even know they have the problem since they don't pay attention, I figured I would share the info with everyone. Hopefully it will solve everyone else's high rev on start up problem also.

JOE

 

[shadowless127]

3rd gen V8's tend to rev high (2000) during a cold start, then goes down to about 1200rpm till it warms, then it drops to about 800-900. I always thought this was wierd (and mine is not the only one that does this) but I guess it's a computer thing.

 

[my98nnj]

Oil change causing a high idle? Lack of oil pressure causing the high idle?

So what your saying is that "if" the ecu detects little or no oil pressure that it's default start up changes to "self distruct mode"? Reving high with no oil pressure?

Makes no sense at all....

 

[JOEZ33]

thats not what I really meant

 

[jammind]

how do u flashed the computer .

 

[JOEZ33]

Since this thread got brought up again I'll provide an info update. The problem came back by itself within a few days of "Clearing the computer". It would start, rev high, then immediately drop to 450rpm, and surge between 1200 and 500 rpm.

I found the problem and fixed it. It was an intake leak at the throttle body. I have to admit, simple problem that I should have found in the beginning. It was sucking in air that wasn't being measured by the MAF sensor. I had a leaking TB gasket, and a loose hose clamp.

Fixed those leaks and problem gone for over a year now.

 

[jammind]

still did not tell me how to flash the computer to a towing mode, from the previous economy mode

 

[JOEZ33]

To flash the computer you have to buy a programmer such as the SCT tuner. Then buy a program to upload to the trucks computer. I bought my programmer used on ebay for around $100 I think, then paid Doug at Bama Chips $50 to write 3 different programs. He emailed them to me and I uploaded them into my SCT Tuner. One program's a 93 octane economy tune, another is 87 octane towing, and the third is 87 economy. Ocasionally I email him and ask for some changes and he sends me an update completely free.

If I want economy I plug the sct tuner into the truck and upload/reflash the truck computer with the economy tune, and a little less power is available. If I want to tow my camper then I upload my towing program. Then it has gobs of torque and shifts harder, and downshifts quicker, and runs much better.

 

[rp23g7]

I bought my 99 EB brand new and its done this high rev at startup ever since i have had it. I thought i was the only one. I am going to check the TB seal and see if that is the issue.

I have tried everything else, mybe the computer flash wil work for me.

 

[napolean]

intake leaks

HI all,
This is my first time in this forum and I need a little help. I'm having a little different problem then what has been mention here,just the opposite,I have to keep playing with the gas to keep it running till it warms up. I just got back from my local ford dealer and was told diagnostics say I have a leak at my PCV Oil seperator. Never heard of such a think,called local parts supplier, neither did they. Does anyone here know what or where it might be. The problem I'm having is hard cool to cold starts. The onboard computer says I have a lean mixture.
Thanks,Napolean

 

[my98nnj]

Napolean, It's most likely leaking intake gaskets, a very common issue.

 

[jseabolt]

Don't know if this is related or not.

I had a weird issue like this on my Jeep Wrangler. I had installed a performance intake system from Turbo City:

After installing their throttle body, intake pipe and filter, the engine reved at about 5000 rpms as soon as I cranked the engine. I disconnected the battery cable for a few minutes and afterwards it's idled fine.

The intake noise was herendous but it did actually make the Jeep go up hills a bit easier.

 

[JOEZ33]

HI all,
This is my first time in this forum and I need a little help. I'm having a little different problem then what has been mention here,just the opposite,I have to keep playing with the gas to keep it running till it warms up. I just got back from my local ford dealer and was told diagnostics say I have a leak at my PCV Oil seperator. Never heard of such a think,called local parts supplier, neither did they. Does anyone here know what or where it might be. The problem I'm having is hard cool to cold starts. The onboard computer says I have a lean mixture.
Thanks,Napolean

I didn't know there was a diagnostic code that specifies PCV. Also didn't know there was an oil separator.....I do have a home made oil separator on mine, which is installed in the pcv vacuum line.

Anyways sounds like you have an intake leak somewhere. Could be the intake o-rings or it could also be just a cracked hose somewhere. I've had the pcv valve pop out before. It's mounted in a wierd position on the SOHC engine. It's hidden between the firewall and the back of the engine. It plugs into a hose instead of the old fashioned way of plugging it directly into the engine. It can pop out pretty easy and cause a huge vacuum leak with lots of hissing noise.