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Discussion Starter #1
I have a 1986 Graduate. I just got the thing running with the help of this BB, but now I have run into a new issue. The car runs fine, drives fine when first started. After the vehicle warms up, the throttle fails to respond. I will be driving along and it will bog down, if I put in the clutch, it will stay running, but the RPMs start bouncing from 1000 to 2000 when the gas pedal is on the floor. I cannot get any response. I shut the car off on the side of the road for about 5 minutes, and the car started right up and ran fine. After about 5 more minutes of driving, the throttle stopped responding again.

I have 2 new fuel pumps (working fine although very loud), replaced spark plugs, wires, cap, rotor button, many new vacuum lines, battery, and fuses.

Any suggestions would be greatly appreciated.

On a side note, I have no headlights, tail-lights, brake lights, or dash lights. Any tips for getting those lights to work?
 

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Toadman5000,
You didn't mention anything about replacing or at least inspecting the fuel filter or air filter. Sounds like the pistons are being flooded and once the plugs dry off a little it can go for a bit more. Just my guess.
 

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1966-2013
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13,741 Posts
Classic AAV stuck WFO action.

Acts like hell when warm, shut down and restart so extra start injection pulses kick compensating for the extra air.

Once the extra pulses stop, throttle goes back to as described.


Check for false air also.
 

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1966-2013
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On the lights, check all fuses and grounds that you can find, regardless of what they are supposed to be related to.

If you have the bullet style fuses, clean the contacts and replace the fuses regardless of how good they appear.
 

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1966-2013
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OH, quick check on the AAV:

Once warmed up and acting goofy, clamp the line between the AAV and the plenum shut with vice grips. (cushion them with small wood or plastic blocks)

If that 'cures' the evil, you have your answer.
 

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air leak -

There are much smarter people than me on this bbd, I don't know how to properly embed a link, so here's GHNL's full post on a similar issue!



Have you seen this page - Bosch L-jet Spider diagnosis ? (the author is not only smart but very handsome...)

My first guess would be air leak in the intake ducts or hoses. All air entering the engine must pass through the AFM (Air Flow Meter) for the ECU (computer) to know how much fuel to squirt. If there is a torn air duct or leaking/missing hose, it will upset that measurement.

Also carefully check the AAV (Aux Air Valve). They can cause all kinds of running troubles. Remove the AAV and put it in the freezer for 20 minutes. The vane inside should then be closed (or very nearly so)*. Next place it in an oven at 150F for 20 minutes. Carefully remove it (use tongs) and the vane should be fully open (or nearly so). If the vane rattles around loose the unit needs to be replaced.

* Also try blowing some air through the AAV when it's cold (just out of the freezer). The vane should block passage of air. I had one fail where the vane appeared to be closed but I could blow through it (around it?) with no resistance. In that case, our Spider would start OK but it tended to stumble under light acceleration/part throttle but run OK with the throttle wide open or at idle. Does that sound similar to yours?
 

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here's GHNL's full post on a similar issue...
Except the info in that reply is bass-ackwards. The AAV is OPEN when cold
(to supply extra air as if the throttle was propped open) and CLOSED when warm. The full thread with corrections is here.

Definately check for 'false air' - all air entering the engine must pass through the AFM (Air Flow Meter). A cracked or loose intake air duct will prevent the AFM from sending the correct info to the computer as to how much fuel to squirt.

Check the wire harness connector at the AFM, too.

I don't think a bad O2 sensor would cause such trouble. The engine would still run fairly well just slightly rich (default setting/closed loop mode).
 

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Discussion Starter #9
Still looking for answers

As you can probably tell by the time lapse between my responses, I don't get alot of time to work on the vehicle (not by choice). But here is what just happened. I took the car out until it got hot, problem emerged, no throttle response, but car would stay idling but fighting to stay alive, if I pushed on the gas pedal, I had no response. The RPMs kept bouncing irradiacally. I left the vehicle running, popped the hood and took a pair of vice grips and two shims and closed off the hose going from the AAV to the plenum. Within seconds, the car died. I tried to restart the car, but would do nothing but turn over. I removed the vice grips and the car started up. I closed the hood and tried to drive on, I only made it 10 feet then problem started again. Now this is where it gets strange. The car would not go forward because I had no throttle response. I put the car in reverse and it went fine. As a matter of fact, I had no hesitation, no problem with throttle response. I thought it was a fluke so I continued to drive in reverse (until another car was coming) and had no issues. As soon as I put the car in 1st gear and tried to take off, no response. I pulled over again, popped the hood and knocked on the throttle position sensor. The vehicle went forward with no issues. I put the car back in the garage and turned it off.

I know that there has to be something with the throttle sensor now at least I think, maybe it was a just a fluke that it ran after I knocked on it, but the fact that it would drive in reverse makes me question.

I don't know what question to ask here except, could the throttle sensor be causing all of my issues? Or is there anything else I can test, try, experiment?

Any feedback would be greatly appreciated.
 

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So, you tapped on the TPS and it ran better? Maybe you need a bigger hammer! (j/k)

I can't explain the backing up OK part of the puzzle but info about the TPS operation and adjustment is in the Spider L-jet page (link is in my signature block). See step #5.
 

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You may want to check your Rev. and Reference point sensors (Flywheel sensors). I had something similar happen to me, all the same symptoms that you mentioned, tach jumping around like crazy, etc. engine was missing and backfiring a bit as well. I didn't try putting it in reverse though, so I don't know if it would have run that way. Had to get towed to the mechanic. Ran fine when he tried, but he checked and cleaned some of the electrical connections anyway. Tried it again, ran fine, couldn't find anything wrong. :confused: He said, "Don't know what to tell you, try driving it around the block and if it happens again bring it back." I got 3/4 of the way around the block and it started doing it again, then it died and I couldn't get it started this time. Of course he wasn't with me to experience the problem, but he came and towed me back to the shop. Started up fine and then acted up again. Finally he saw what it was doing and that I wasn't crazy. He checked a bunch more stuff, all the the things mentioned here I imagine. He finally decided it was a faulty sensor. He had a used one that he put on the car and it ran fine. I asked him if I should get a new one instead of the used one. His answer was he could order me one, doesn't usually have to keep new ones on hand because they're a bit expensive and he doesn't usually have problems with these sensors. I asked him if it would be better to have a new one instead of a used one. His response not necessarily, this is one of those parts where either they work or they don't. Is this true? Well, I didn't get a new one and I haven't had this problem happen again. He gave me the old sensor so I knew what to get and have a spare. The cool thing, he didn't charge me for his time, labor, or the sensor he put on.:D Funny thing is, I checked my old sensor and it read 0.93:rolleyes: Anyway something else for you to try. Alright sorry for torturing everybody with my story, but I just wanted to show that for as much as I distrust and hate having to go to mechanics and doctors, sometimes they're pretty cool. I could have had a $250.00 dollar charge for the day instead of just $50.00 for the tow.
 

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The sensors are usually a work/don't work item. But they can become loose where they are attached to the bell housing or the electrical connectors could have an iffy connection. Either (or both...) of those faults might cause an intermittant problem.
 
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