RPM Drop/Surge

[gtyates]

Recently I made a posting about an idle/rpm issue. The idle issue is basically resolved after a gasket leak was found at the egr inlet tube into the air intake. But I have a more perplexing issue that so far no one has been able to resolve. Basically what is happening is when I left my foot off of the accelerator (such as cruising down a hill) I get an immediate drop in rpm's to about 1000 on the tach, followed by an immediate attempt to increase rpm's on its own where it should be (say @ 45 mph tach is around 1600-1700) As the rpms attempt to increase there is an actual surge (ranges 200-300 on the tach) before I either push the accelerator to continue driving or press the brakes to stop for a red light, etc.. Either situation will put the truck back on steady rpm's. The shop I use has hooked it up to their monitors twice and nothing shows as a problem, even for a split second. Mechanic felt it when he drove it, but can't find it. I have replaced the MAF, IAC, and Air Charge Sensors, all with Motorcraft parts, but this has not resolved the issue. Also fuel pressure is perfect. Any ideas? Could the TPS be doing this but the "blip" is so short the monitor does nto pick it up? No CEL is present. Truck has the OHV engine with 111k miles. Ambient temp does not impact this issue.

 

[gtyates]

Well, still chasing the "ghost" in my system. Just replaced the engine coolant temp sensor. Idle seems to be a bit smoother and hot start issue seems to be resolved, but still getting the odd rpm drop/surge issue. I am running out of sensors to replace.

 

[dean1997sport]

I am having the same problem but when I let my foot off the gas it just drops to 1000 rpms with surging only once in a while not every single time.

 

[gtyates]

Glad I am not the only one with this issue. lol!!! It is very frustrating!! Coolant temp sensor did not help the surge, though it did help overall idle and the hot start issue.

 

[dean1997sport]

well I posted my problem in the transmission section so from what I found out it the TC unlocking now why its unlocking I never got an answer but it was suggested that I should check my TPS.

 

[gtyates]

The shop that works on mine also thouht it was the tourque convertor unlocking but computer scans were not showing an issue. I too wonder if the TPS is causing this issue. Whatever is causing it is such a quick "blip" the computer in the truck as well the external scans is not detecting it enough to show a fault. Are you going to try the TPS replacement? So far I have replaced MAF, IAC, INtake Air Temp sensor, engine coolant sensor. Previous work on mine has included plugs & wires, fuel filter, camshaft position sensor and sychronizer. The only thing that the scans indicated at the shop was that I have an O2 sensor opening a little slow but they did not recommend replacing since it is not setting a fault code. Overall my truck has been solid since new, but this issue is frustrating!!

 

[dean1997sport]

Yea I am going to check it first.
But yea I have done every thing you have too except MAF mine seems ok.
It really bugs me too but ithe TC is definitely un locking thats for sure.
The only time it does not do it is when I am doing like 70 on the freeway, it still drops a bit but not all the way to idle.

 

[gtyates]

I noticed on mine today that I experienced the surge slowing down from about 55 on one of our local parkways. I took my foot off of the gas pedal to begin slowing down. Immediately rpm's dropped to about 1000, then surged their way back up to around 1700 or so. When I put my foot on the brakes rpm's smoothed out and stayed smooth all the way back down to idle as we came to a stop. Idle is fine btw, hold relatively steady at about 800 on the tach.

 

[2000StreetRod]

TPS test procedure

If you have a voltmeter it is easy to test your TPS for "drop outs" or other erratic behavior. An analog meter is better than a digital meter to find erratic behavior since it has an instantaneous response. Several members have experienced weird performance due to a faulty TPS. See My Helpful Thread TPS Test Procedure

When the PCM switches from closed loop to open loop it unlocks the torque converter. The PCM compares the MAF sensor output with the TPS output to check for reasonableness.

Another possibility is your EGR valve. The PCM closes the EGR valve when it detects closed throttle from the TPS. The engine will run rough at closed throttle with the EGR valve open. If I'm driving 20 mph on a level road with the window open and release the accelerator I can actually hear my EGR valve close.

 

[dean1997sport]

Ok I called the parts place TPS is $22.00 w/ 2 year warranty I will get one on the way home tonight and pop it in a report back.

 

[gtyates]

dean1997, any updates? Put in TPS yet? And if you did, how did you get the old one out? I understand they use locktite on it when initially installed.

 

[dean1997sport]

Ok I got it late yesterday but I had taken it off before just use the right size screwdriver and you will be ok. Well it did improve the shifts a lot firmer than before and the TC is not unlocking at any speed over 50, it did not change any thing under that my TC is still unlocking when i let off the gas anywhere between 30-50 mph. It was worth it just for the better shifts.

I think the question I want to ask next is this a normal condition? do all explorers do this? is the TC supposed to unlock in this way? maybe we are trying to fix something thats supposed to happen?

 

[gtyates]

For my truck this is a relatively new issue. I began noticing this maybe 6 months ago. My truck has been in our family since new. My Dad & Mom bought it new and I took it over last year when Dad bought a Lincoln MKZ. I had a '97 with the OHV and it never did this all the way up to 140k miles when Dad traded it toward the Lincoln and I took his because of the much lower mileage. So sounds like the TPS may have helped, but not solved the problem, correct? Frustrating!! How many miles do you have on yours? Mine has 111k, very low mileage for the year. And truck has been very well maintained since new.

 

[dean1997sport]

Yes I think it was worth it just for the shift improvement but it did not completely solve the problem. I am now looking for any vacuum leaks.
I bought mine used with 120K on it. It now has 179K and its been a good truck so far just these minor issues.

 

[gtyates]

What did you have to do to get the TPS screws loose? I actually tried to loosen mine and could not get the screws to budge. As a matter of fact the screw head was starting to ream out a little so I gave up.

 

[dean1997sport]

Oh man that happened to me you need a impact driver
they look like this you can get them pretty cheap.
I had one on stand by just in case but I had to crawl up in there and just push really hard and turn but if it looks like its going to strip use the impact driver
Here is what it looks like check the link

http://www.harborfreight.com/impact-screwdriver-set-with-case-37530.html

 

[gtyates]

Well I am going to try and replace the TPS. None of my local parts shops have one in stock so I ordered a Motorcraft one from rockauto. Hopefully by the end of the week I will know if this helped. Again, what is so crazy about this is the fact the 2 computer analysis have not found an issue with the system, though everyone including the shop I use can both see on the tach and feel the drop/surge when it happens. Overall these Ex's are solid vehicles. My only issues with this one or the '97 that I had were always sensor related. Engine/tranny were solid on both of them. At least the OHV engine is.

 

[gtyates]

Received my TPS today from rockauto.com. Not bad, ordered on Sunday received on Wednesday. Anyway, huge difference in performance of the truck!!! While not ready to say this has cured 100% of the surge issue yet, after 2 long drive cycles no sign of the surge is present!! Only thing I now notice is a little driveline shutter now which I suspect may indicate the 5th shock needs to be replaced. It is 15 years old. lol!! When I replaced the main shocks I did not even think about the 5th shock on the rear axle. Will update if this did not cure the "ghost" in my system, but looking good so far.

 

[gtyates]

I spoke too soon. Most of the surge is gone, but not all. I seem to be noticing it as it shifts in and out of O/D. Tranny fluid looks great with no odd smell, but this concerns me some on the tranny. Truck was hit in rear about 3 years ago when my Dad still owned it. Though he never noticed any issues with shifting (though coincidentally the 4x4 shift motor died a week or so after repairs were done) I am wondering if this might be somewhat related, maybe force of accident has hastened the demise of something internal to tranny. He drove it as a weekend cruiser/travel vehicle, never as a daily commuter in stop & go traffic like I face daily, so he never noticed an issue. And tranny has been serviced regularly since new. Truck only has 111k on it now. But between computer analysis and smoke test for vacuum leaks I think just about anything engine related can be ruled out now as the cause.

 

[dean1997sport]

Yep I still think it has something to do with the VB and the solenoids I have been doing a little research on VB rebuild ( check the transmission forum) and you can get a rebuilt one or do it your self. That is what I am leaning towards right now the TPS did make it shift better but didnt do hardly anything to cure my TC from unlocking.