throttle response when started

This sounds like you have an Idle air motor that is slow or sticking. It rarely sets a code and most people miss-diagnose the problem.

IAC (idle air motor) motor. They are bad about going bad and will cause the truck not to idle and they are always worse after the truck sits for a long while (like over night). I replace a lot of them for this problem. They are fairly easy to replace. The IAC is located on the intake. You should also consider cleaning the throttle body with a spray type cleaner to remove any carbon build up on the throttle blade.

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3. Disconnect the IAC valve electrical connector.

4. Disconnect the throttle bypass hose.

5. Remove the bolts, the IAC valve and the gasket.

6. NOTE: Install a new IAC valve gasket.

   To install, reverse the removal procedure.

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Still doing the same thing but not as bad, still tries to idle at 500rpm roughly, then it will jump to 1500rpm and drop down to 1000rpm and run great.

Did you clean the throttle body also? Have you checked the engine good for vacuum leaks? Do you have a scan tool?

Take the mas-air flow sensor out and clean it with brake cleaner let it dry completely then reinstall.

Edited by tactgear1 on June 29 2006 at 11:41pm

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Relist: I want a different opinion.
If it was a vacume leak or MAF sensor why would my ranger only run rough for just a few minutes after it sets for 30 to 60 minutes,or over night,Has no throttle responce except making it want to die. if I start it right back up it is ok,wheather I drive it in town (stop and go) or on the hiway, so far every one has just been taking shots in the dark that I could have done myself with out the expence.So far throttle position sensor,IAC valve, cleaned throttle body it looked and felt good, new plugs(motorcraft platinum)Cleaned MAF(don't have ohm meter) no vacume leaks so far. Is there anything about the Ford service bulliten I mentioned(wiring haeness on the driver side frame;posable chaffing and rubbing through;it is a little rubbed but dosn't look like it's went through the cover).

I am sorry that I have not given the answer to fix the problem , I am however at a disadvantage over the net. I try to cover the basics first. The problem sound like a fuel pump problem but you say that it is good if you are not positive purchase a gauge and monitor the pressure during the problem. I have attached the bulletin that is for the harness problem. I will also forward this to my car category mentor for second opinion. If you have any questions please feel free to ask I can furnish you with specs diagrams whatever you need to help repair the truck.

Various drive-ability or engine performance concerns may be present. These concerns could be:

• Hard to start
• Engine hesitation
• Rough or unusual rolling idle
• Lacks power
• Slight engine surge
• Slight rpm fluctuation at various speeds
• Engine knock
• Engine stumble

These may be caused by an electrical wiring harness that is being chafed by the under carriage around/under the driver's seat area.

ACTION:

Inspect affected wires and determine if chafe is present. If chafe is present, refer to the following Service Procedure for details.

SERVICE PROCEDURE

1. Inspect wire harness and inspect for wire chafing. If chafing is present, proceed to Step 2. If not, proceed with other normal electrical/drive-ability diagnostics for repair.
2. Remove wire harness interface bracket (connector retaining bracket -14A206- (driving board bracket))
3. Verify Mastic Insulator Patch (F87Z-1310484-AA) is present. If mastic patch is not present, proceed to Step 4. If patch is present, proceed with other diagnostics.
4. If wire chafing is evident between rear of connectors and the start of convolute, repair damaged wire with known wire repair service procedures. Protect repaired wires by applying Flex Wrap (F2TZ-18K459-AA) to affected area. Secure flex wrap with electrical tape or equivalent.

   NOTE: <>CHAFING COULD BE PRESENT FORWARD OF THE CONNECTOR ABOUT 3' (0.9M) FROM THE CONNECTION OF THE -14405- AND/OR -14334- WIRING ASSEMBLIES ON 1998 RANGERS.

5. Clean surrounding area on underside floor pan reinforcement and apply new mastic patch to the clean area.
6. Reinstall harness interface bracket.

   NOTE: <>IF BRACKET IS DAMAGED, INSTALL NEW DRIVING BOARD BRACKET (F87Z-14A163-DA FOR 1998 USAGE OR XL5Z-14A163-AC FOR 1999 USAGE). TORQUE BRACKET TO 8 N-m (6 lbs-ft).

7. Verify repair with road test.

F87Z-1310484-AA Mastic Insulator Patch

F87Z-14A163-DA Driving Board Bracket (1998 Vehicles)

XL5Z-14A163-AC Driving Board Bracket (1999 Vehicles

F2TZ-18K459-AA Flex Wrap

Edited by tactgear1 on June 30 2006 at 10:16am

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The dealers mechanic checked the fuel pressure while this problem was happening and the fuel preesure was good.