Idle Issue

[gtyates]

Another idle issue thread. My '96 with OHV is having some idle related issues.

Idle in gear or park hangs around 900 all the time. But under load, such as braking or sharp turns at low speed the idle will drop to the 500 range.

Several things have been done so far as follows:

Upper intake gaskets replaced as well as cleaning throttle body. Had a CEL for lean condition.

No CEL is present, but shop did observe the MAF was reading a little low, so cleaned it.

Cleaned IAC valve. The one on it is about 8 months old but did have carbon build-up.

Negative battery was loose at battery, so I have tightened it.

Camshaft position sensor replaced about 3 months ago.

Could the IAC be bad already?? I pulled it off and had wife turn key to on poisition. It did move inside, though seemed to be a little delay. Also made a "popping" sound.

Still no CEL present.

Thanks for any ideas.

 

[gtyates]

Following up. Replaced IAC. Has helped significantly!! Bought a Motorcraft unit this time instead of the parts store brand. Still having a little issue with some idle drop when taking foot off of gas at cruising speed. Drop is not near as dramatic as it was with old IAC though, and idle recovers very quick now. Could the low MAF sensor reading low be adding to my issue? Again, shop did a complete diagnosis and it did show the MAF sensor reading low, but still in spec. Maybe this is part of my problem? To me truck just does not run smooth when cruising and seems to hesitate a bit. Also brakes feel a little spongy as well. And still no CEL, so whatever it is it is not enough to throw a code. Frustrating!!

 

[1998Explodasport]

Did you try cleaning the MAF?

 

[gtyates]

Yes, cleaned it. No change. I also pulled negative battery cable after replacing the IAC.

 

[1998Explodasport]

Maybe you have a fuel probem have you checked the fuel pressure? When was the last time you replaced the fuel filter?

 

[gtyates]

Fuel filter changed back in the fall. I am leaning toward the low MAF reading maybe indicating the MAF is close to failing. When the shop hooked it up and watched the system the only things showing even slightly off were the low MAF reading (at lower end of specs) and 1 o2 sensor also reading slightly off, but in spec. Though the shop is not a Ford dealer they still have a very thorough scanning system. I have been using them for many years and they have always been honest with me on repairs. They did not necessarily recommend replacing the MAF, hoped cleaning would improve the issue I am having. The MAF is original to the truck, so it is now 14 years old with 110k miles on it.

Thanks for all ideas.

 

[2000StreetRod]

MAF sensor voltage vs RPM

When the shop decided your MAF sensor voltage output was low was that compared to a stock MAF sensor at the low RPM?

When was the last time that you replaced the spark plugs?

Did you add fuel injector cleaner to the tank after replacing the fuel filter?

You may consider replacing the PCV valve.

 

[gtyates]

Thanks for latest suggestions. Plugs and wires done in the fall. Fuel injector service done at time filter was changed. PCV valve also done in the fall.

Measurements on the MAF were based on specs for our Ex.

What is making me think it is the MAF is that right now this issue is intermitent. Sometimes when I left off gas at cruising speed the RPM drop is nice and smooth, and sometimes it drops instantly and then recovers. The dropoff is not as bad now with the new IAC, so I assume the new IAC is making up for some of the issue. I sure hate buying a new MAF, but might not have a choice.

I have read at other places one test I can do is to unplug it and see how the truck runs. If no difference it is probably the MAF, but if it runs worse when unplugged this might not be the problem.

Keep ideas coming.

 

[gtyates]

So, I unhooked the MAF and let it run. Truck ran the same either way, with only difference idle was slightly higher with the MAF unplugged. So, I am now leaning toward an almost dead MAF.

Any other ideas?

 

[gtyates]

After thorough cleaning of MAF, resetting system by pulling negative battery cable, and having several driving cycles the RPM drop-off with lifting foot off of accelerator at cruising speed as well as uneven idle has not cleared up. So, based on shop telling me the MAF was reading low and everything else scanned as in spec I am replacing the MAF. Paid a little more and bought a replacement new Motorcraft part through rockauto.com. Hoping this and the already new IAC resolve the issue.

 

[1998Explodasport]

After thorough cleaning of MAF, resetting system by pulling negative battery cable, and having several driving cycles the RPM drop-off with lifting foot off of accelerator at cruising speed as well as uneven idle has not cleared up. So, based on shop telling me the MAF was reading low and everything else scanned as in spec I am replacing the MAF. Paid a little more and bought a replacement new Motorcraft part through rockauto.com. Hoping this and the already new IAC resolve the issue.

If the truck ran the same with the MAF unplugged then most likely the MAF is good. I had a few good MAFs around my garage I could have sent you for the price of shipping.

 

[gtyates]

Update. Got my MAF from rockauto. Pulled negative battery cable, installed MAF, used dielectric grease on all connections, then hooked battery back up. Have taken one drive cycle so far. Incredible difference!! No more hesitation on acceleration. Still getting a little rpm drop when I lift foot off accelerator, but not near as pronounced as before and it is not causing truck to lope. So maybe the IAC and MAF have resolved the issue. I hope!! This is challenging because whatever is causing this issue is not throwing a code, so my computer is adjusting to the reading it is receiving. Brakes also feel less spongy!!

 

[gtyates]

Well, I spoke too soon. Even after replacing the MAF I am still getting some RPM drop when taking my foot off of the gas. But, it does not happen every time. And still no CEL on. I also am noticing the idle speed, at times it is around 900 when in gear and at times it is around 750 (tach indicated) with a/c on and sitting with steering wheel pointed straight. I have checked every electrical connection I can see/touch/feel in engine bay and I did find the TPS connector was not completely pushed on. I have since shot a little dieletric grease in it and reconnected. I have noticed since doing that it did drop less today than it has been, but still did experience a drop when taking foot off of gas, as well as a slight (maybe 100rpm) surge. Very strange indeed. Is there some really good diagnostic software with a connector to the OBDII port and my laptop anyone can recommend? I would be willing to hook it up and drive it and see what it is reading.

Or, does anyone have any idea what is causing this? I can't believe of the millions of Ex's out there I am the only one experiencing this. lol!! But with my luck, when I have a problem it is never "normal".

 

[jremington59]

If it were me I would pull the plugs and see what they look like. What brand plugs and wires did you buy?

 

[gtyates]

Plugs and wires are Motorcraft. I am wondering if the TPS (throttle position sensor) is acting up enough to cause this but not enough to trip a CEL?

 

[jremington59]

If you think everything else is good I'd get the fuel pressure checked. You also could try running some good injector cleaner through it.

 

[gtyates]

RPM Drop/Idle Issue

Thanks for suggestions. Injector service was done back in the late fall, when tune-up was done. This is frustrating!! I actually wish it would trigger a CEL!! As I research TPS symptoms what I am experiencing seems very similar. I don't have a voltmeter, so can't do official measurements. So far replacing the IAC (which was dirty) and the MAF (which shop said was showing low, but in spec) have helped, but issue still exists. I chose to replace those parts, shop did not yet recommend any replacements. Again, idle at times is around 750 in gear while stopped and sometimes closer to 900. And on occasion (but not every time) I get a very fast RPM drop when I take my foot off accelerator (say a drop to less than 1000 then a quick recovery on its own) to stop the truck or even to just to ease off the gas after topping a hill. Has anyone had a failing TPS with similar symptoms before a total failure?

 

[gtyates]

Maybe related question. I have been reading on this site about a throttle cable modification using zip ties on the end. Just checked mine and with the gas pedal pulled all the way up I had at least an inch of slack cable past the spring. And, when fully pressing the pedal the spring was only showing very slight compression. So, I put 2 zip ties on the cable, still leaving about 1/4" of slack. Will drive the next few days and see if it makes any difference. Gas pedal definitely feels tighter just pushing it with truck turned off. Don't know if this will impact my rpm drop but I sure hope the truck is more responsive.

 

[gtyates]

Did the throttle cable mod. Truck is much more responsive, and idle does seem better overall. I opened the throttle body and now when pressing the throttle all the way down the throttle body completely opens up. So, response is better, idle seems better, but, still getting the rpom drops when letting off the accelerator. I notice it the most in situations where I have topped a hill and then let off the gas to stay close to speed limit as I go down the other side of the hill. I also notice the rpm's drop, and then raise back up, but there is a surge (maybe 100-200 rpm) before it recovers to where it should be for cruising speed. Very strange indeed. And still no CEL. I am starting to lean toward the fuel pressure issue that has been suggested. Anyone else experience this?

 

[gtyates]

I am leaning stronger to the fuel pressure regulator being the issue. I am now experiencing a very rough idle on start-up after the engine is warm (example, go to store, shop, get back to truck start it and it runs very rough until I give it gas with the pedal). About ready to take to the shop again and ask them to ck fuel pressure. Of course still no CEL. If it is the regulator I guess it makes sense for rpm's to drop out when I take the foot off of the pedal to slow down the truck. Gas mileage has dropped some, but not terribly, down about 1mpg around town to 14.

Thanks for ideas so far. if I get it figured out I will follow up.