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218lb Lap Timer
 
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Join Date: Sep 2004
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Unhappy 84 Carrera Throttle Flat Spot @2900

Cool mornings, cool motor. I have a flat spot in the throttle of my 84 carrera coupe (3.2). It revs up to 2900, hesitates, and then the throttle seems to kick in and surge the vehicles forward if I stay on the accelerator. If I maintain the throttle at 2900, the motor seems chaotic; hesitating, surging, hesitating... You get the picture...

Hot days, and when the engine is warm, this problem seems transparent.

Any suggestions would be appreciated...

Thanks

-Jojo
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-21-2004, 09:01 PM
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There is some posts about this. It could be a vacuum leak in hose going to the fuel pressure regulator. This makes it run rich at part throttle.
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Old 09-21-2004, 09:14 PM
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JCTmuga;

I got an 84 Carrera with the same exact problem. Bucks about the same place as if I am tap dancing on the gas pedal. If I am driving around through the gears, it shows up as hesitation. Under 3,000 RPM seems to be the problem area.

Is your idle wobbly too?

Here what I've done to no avail:

New Bosch 4+ plugs
New cap and rotor
New Clewett Eng. plugs wires
Valve Adj.
Checked head temp sensor: 1536 ohms after sitting 5 hours
Cleaned and tested idle positioner valve, tested ohms
Checked hoses for leaks
Checked fuel rail pressures, all perfect
Checked fuel pump amp draw, perfect
Ran BG44K thru tank
Cleaned out DME connector

Oil cap does show a tired rubber gasket, so that goes next.

Some suggest the ambient air valve that was updated for late 86 as shown in Panorama 11/01. Of course, one that I don't have. If someone has that soft copy, please paste it or a link.

If any body has any insight on this very common Carrera problem, please write on. It is frustrating.

PM me your email address so I can email you if I find the cure first.


Indigowhale.

Old 09-22-2004, 04:22 AM
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Check your O2 sensor and adjust the AFM.
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84' 3.2 Targa
Old 09-22-2004, 04:58 AM
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Dan,

AFM = air flow meter? how do you adjust it? do you mean test it for ohms through its movement without a break in signal?

Thanks.

Indigo
Old 09-22-2004, 05:02 AM
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Indigo,

Yes the AFM is the Air Flow Meter. There's a small access hole on the bottom left front corner. It may have a cap over it. Under the cap is a screw that adjust the meter/mixture. You can test the unit but I don't know that that will tell you if the mixture is correct. I believe that the shop will put a gas analyser on the car and check the mixture measurement during adjustment. I may be wrong here and I'm sure more knowledgable people will chime in if I'm incorrect. I think your symptoms are identical to what mine were, but you be the judge.

Here's what mine did: Severe stumbling/bucking at about 3000 RPM especially when cold and in lower gears. Hesitation or flat spot between 3500 to 4000 RPM. Felt like a lack of gas almost if you accelerate slowly through the range. If you put your foot into it symptoms would almost go away completely. Replacing the O2 sensor cured the stumbling but I still had some of the flat spot. Once the AFM was adjusted it's gone completely.

That's my story but your's may be slightly different. Hopefully more food for thought in chasing down your problem.
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Old 09-22-2004, 07:23 AM
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218lb Lap Timer
 
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Indigo,

It seems as though we have a similar problem. I did some searching through past forums last night for suggestions. I found this thread that seems to have good advice.

Need Help w/Testing

my email is jtcmuga@yahoo.com for further correspondence.

I'll be working on this problem over the weekend: checking AFM as well as adjusting my valves.

Things that I have done so far...
cap, rotor, plugs, wires, check cylinder head temp sensor, checked 02 sensor.

So, you are a bit ahead of me on the troubleshooting, but we're following a similar path.

I haven't heard of the Ambient Air Valve suggestion. I'll see if I can find that article in Panorama.

Good luck Indigo, and I'll be sure to report all progress.

Thanks for your help, Dan, I'll be checking my AFM very soon...

Joe C
'84 3.2 Carrera Coupe
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-22-2004, 07:56 AM
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Indigo,

My idle is wobbly at startup, but will settle even when the flat spot is still present.

Jojo
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-22-2004, 07:59 AM
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Guys...'84 Carrera owner here, contact Steve Wong at 911chips.com for a performance chip (actually revised code for the DME). Cures the flat spot issue, its inherent to the car, I know exactly what you are referring too...
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Old 09-22-2004, 08:02 AM
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Thanks BG

I have an 86 stock DME Chip laying around, was all charged to go and replace the 84 chip, got the thing apart and noticed it was soddered in. I am going to ask my Chevy friend to replace it, he is a electronic tech.

Seems like another person fixed the problem by replacing the DME after it received 18 volts, well mine had that problem before the bucking and hesitation. Now new regulator but problem persists.

Also, I will try the water decarbon as mentioned in todays dealer rip off thread. Figure for free I can improve the idle a bit--and maybe ruin the CAT?

I will be at it over the weekend, so I'll let you all know progress. I am almost ready to put down for the Wong chip, but don't want to be at the same place I started. Thanks for the advise, everywhere I read about this flat spot on the carreras.

As far as the AFM, yes the CO has to be set correctly, but mine passed emission well under in this category....I'll post results later.


jtcmuga: my email is arivera911@yahoo.com in case you hit gold over the weekend.
Old 09-22-2004, 08:20 AM
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thanks BG, i definately plan on getting one of steve's chips, but want to wait until i upgrade the exhaust.

i'll be in touch, indigo.

jojo
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-22-2004, 11:57 AM
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Here's a link for refurbishing your air flow meter:

Free HP Increase for your 3.2

But I still think its ignition related.

How do your plugs look?

Joe
Old 09-24-2004, 09:34 AM
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Thanks for the air flow meter tip... I just changed my plugs, cap, rotor, and wires, so they should be fine. I'll double check those components when i adjust my valves tomorrow.

Thanks again
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-24-2004, 12:22 PM
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Same here, all new ignition. Same problem persists.

Have left idle positioner off and it idles better and no bucking. Piece of worthless crap, but we will see how the car behaves when it is cold. For now, it is staying disconnected.

Once all else is rulled out, the Steve Wong chip may be needed to get a Weber like feel instead of the injection lag.

Flat spot is less pronounced but there. No bucking yet. I think the piston inside the IPV is floating at its will causing the problem.
I intend to take it out completely to rule it out alltogether.

What is ther relation between the IPV and problems not at idle? does it introduce unwanted air at the wrong time? Or does the DME tell it to by mistake?
Old 09-24-2004, 03:32 PM
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Also clean and reset the gap for the flywheel speed & reference sensors
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Old 09-24-2004, 04:32 PM
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Jojo,

Is your head temp sensor still the single wire type? If so that could be your problem.

Joe
Old 09-24-2004, 05:59 PM
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If you get the chip from SteveW, get the 4k program and the simple instructions on how to modify your circuit board. This 4k program gets rid of the sub idle dip when the engine decelerates and also make for smoother throttle response. The mod is simple. Ask Steve as he can explain the beneifts better than I.

Jeff
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Old 09-24-2004, 10:09 PM
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Thanks for all the info! This is great. My troubleshooting list is huge. Joe, my cylinder head temp sensor is the single wire type.

I'm sure I'll get to the bottom of this fast...

Thanks again.
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-24-2004, 11:19 PM
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218lb Lap Timer
 
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Fellas,

No solid news on the throttle flat spot. I gave the 3.2 a valve adjustment. It was ~90 degrees outside and sunny all weekend and didn't notice the flat spot in the throttle. The engine feels like it is running stronger, I hope it isn't psycological because I just spent many hours busting my knuckles and getting down and dirty under the car and want some sort of gratification.

Joe, i don't know of any other cyl head temp sensor than the single-wire one... please advise...

Overall, I'm expecting the flat spot to show up tomorrow morning when it's cool, so I'm still working on it...

Take care all...

Jojo
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'84 3.2 Carrera Coupe
'00 Jeep Grand Cherokee LTD

"If everything seems under control, you're just not going fast enough" -Mario Andretti
Old 09-26-2004, 09:31 PM
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I found a flat spot caused by a worn area on the AFM potentiometer material. It was contributing to a rough idle.

Rather than buying a new AFM, I had it refurbished, which included replacing the potentiometer and all the innards. Now I've got no AFM worries for awhile.
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Old 09-27-2004, 08:46 AM
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