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78 FI Super terrible idle when cold.
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vertsteve
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PostPosted: Fri May 07, 2021 1:39 pm    Post subject: 78 FI Super terrible idle when cold. Reply with quote

Hi All, I have a 78 FI Super that I have been trying to get dialed in. When the car is cold or cool, it does not want to idle correctly and when given gas it bogs down and wants to die. It does this at first startup from sitting overnight and also after sitting for a couple hours after a drive. When warmed up the car runs great, idles great, and has good throttle response. So this issue is only when the engine is cooled off. I have replaced all the vac hoses, S boot, injector seals, head temp sensor, and fuel pump relay. It does have EGR that has the filter missing to the exhaust, I plan to delete this entirely, I have removed and plugged the vac hose to the EGR but no changes result. I have unhooked the CSV and even crimped off the fuel line still no changes.

Any help would be greatly appreciated as the weather is nice now and would like to get out and enjoy some drives without having to worry about trying to get the car fully warmed up just to go anywhere.

Thanks,
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busdaddy
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PostPosted: Fri May 07, 2021 2:46 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

Any black smoke from the exhaust when it's acting up?, what happens when you unplug the TS2 (head temp sensor)? , ever done a fuel pressure test?
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vertsteve
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PostPosted: Fri May 07, 2021 2:52 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

busdaddy wrote:
Any black smoke from the exhaust when it's acting up?, what happens when you unplug the TS2 (head temp sensor)? , ever done a fuel pressure test?


No black smoke, just rough idle and then starts to clear up after warming for 5-10min. After a drive and a cool down its hard to get started again and keep running until warmed up again. Once warmed up it runs great.

I have not noticed a change when unplugging the TS2 that I recall. I have not ran a fuel pressure test either as I didn't think this was an issue since it runs great when warm. I do have a replacement FPR if needed though.
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mouser98
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PostPosted: Fri May 07, 2021 2:59 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

Does that FI have a "5th fuel injector" that sprays fuel into the throttle body when it's cold like the later Rabbits?
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vertsteve
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PostPosted: Fri May 07, 2021 3:02 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

mouser98 wrote:
Does that FI have a "5th fuel injector" that sprays fuel into the throttle body when it's cold like the later Rabbits?


Yes it does the Cold Start injector has been unplugged and fuel line blocked off but still does the same symptoms during the tests.
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busdaddy
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PostPosted: Fri May 07, 2021 4:36 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

That cold start injector (CSV) only operates when the starter is cranking, and then only if the thermo time switch (TTS) thinks it's cold enough to need it.

No change when unplugging the TS2 is telling us something, it should go pig rich instantly (black smoke and nearly dying), a fuel pressure test would by my next move. A 0-50 lb water pressure gauge from the hardware store will work, you'll also need a Tee if your CSV has 2 nipples on it, 5/16" hose barbs are needed to connect it. We need to know the pressure with the vacuum line to the fuel pressure regulator down on the tin ahead of cylinder #1 (FPR) connected as well as disconnected, bonus points for a reading with the return line above the starter pinched. You can also do this test with the engine at rest by depressing the flap in the air flow meter (AFM) while the key is on (green wire off coil to prevent cooking points), although you'll need a hand vacuum pump to test the FPR's vacuum response.
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PostPosted: Fri May 07, 2021 4:54 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

vertsteve wrote:
busdaddy wrote:
Any black smoke from the exhaust when it's acting up?, what happens when you unplug the TS2 (head temp sensor)? , ever done a fuel pressure test?


No black smoke, just rough idle and then starts to clear up after warming for 5-10min. After a drive and a cool down its hard to get started again and keep running until warmed up again. Once warmed up it runs great.

I have not noticed a change when unplugging the TS2 that I recall. I have not ran a fuel pressure test either as I didn't think this was an issue since it runs great when warm. I do have a replacement FPR if needed though.


Air auxilary Regulator or Valve needs to get tested. Sounds like it is closed when cold. Once the engine gets warmed up it is fine since it is closed. Hard start, again, it is closed. All is pointing to the AAR or AAV.
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busdaddy
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PostPosted: Fri May 07, 2021 5:10 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

VW_Jimbo wrote:
vertsteve wrote:
busdaddy wrote:
Any black smoke from the exhaust when it's acting up?, what happens when you unplug the TS2 (head temp sensor)? , ever done a fuel pressure test?


No black smoke, just rough idle and then starts to clear up after warming for 5-10min. After a drive and a cool down its hard to get started again and keep running until warmed up again. Once warmed up it runs great.

I have not noticed a change when unplugging the TS2 that I recall. I have not ran a fuel pressure test either as I didn't think this was an issue since it runs great when warm. I do have a replacement FPR if needed though.


Air auxilary Regulator or Valve needs to get tested. Sounds like it is closed when cold. Once the engine gets warmed up it is fine since it is closed. Hard start, again, it is closed. All is pointing to the AAR or AAV.

Normally I'd agree, but the bold part of this statement says there's more going on than just an AAR issue:
Quote:
When the car is cold or cool, it does not want to idle correctly and when given gas it bogs down and wants to die.

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PostPosted: Fri May 07, 2021 9:26 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

busdaddy wrote:
VW_Jimbo wrote:
vertsteve wrote:
busdaddy wrote:
Any black smoke from the exhaust when it's acting up?, what happens when you unplug the TS2 (head temp sensor)? , ever done a fuel pressure test?


No black smoke, just rough idle and then starts to clear up after warming for 5-10min. After a drive and a cool down its hard to get started again and keep running until warmed up again. Once warmed up it runs great.

I have not noticed a change when unplugging the TS2 that I recall. I have not ran a fuel pressure test either as I didn't think this was an issue since it runs great when warm. I do have a replacement FPR if needed though.


Air auxilary Regulator or Valve needs to get tested. Sounds like it is closed when cold. Once the engine gets warmed up it is fine since it is closed. Hard start, again, it is closed. All is pointing to the AAR or AAV.

Normally I'd agree, but the bold part of this statement says there's more going on than just an AAR issue:
Quote:
When the car is cold or cool, it does not want to idle correctly and when given gas it bogs down and wants to die.


I do not disagree with you. I think you are spot on. BUT, let’s stay with one symptom at a time, until it is proven incorrect. Because ONLY through elimination can we further define the actual issue.

I actually am in agreement, like it has a massive vacuum leak, a bad regulator or a plugged fuel filter. But before going there, I would still adjust valves, change the oil and check the points and plugs.
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MuzzcoVW
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PostPosted: Mon May 10, 2021 3:23 am    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

I'm thinking possible vacuum leak also. One thing I've found with these is that they're already tuned on the edge of too lean, Introduce any extra air and instant issues. Are all the hoses on the intake including the ones to the air filter housing in good shape and connected properly? When I restored my 75 back to FI it was found that three of the AFM I have were tuned lean. After making the proper adjustment with a sensor I never have the cold start issue anymore. Remember, some of these cars had this problem when brand new
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PostPosted: Mon May 10, 2021 4:58 am    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

I wonder if backing off on the idle bypass screw on the AFM will help. I had minor issue in 50-65F range where the my 76 would pop to life on first crank then die. Second crank and would run better.

I backed off the bypass one full turn to let a bit MORE air past the meter and seems to be better. Think the TS2 was calling for more richness than the outside temps warranted, at least for my setup.
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PostPosted: Mon May 10, 2021 11:38 am    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

Following
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PostPosted: Thu May 13, 2021 1:04 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

Never mind what I said about the idle richness afm adjustment. I had the start up then die symptoms again.

The obviously much brighter previous posts were right in at least my case. I put in a spare aav and better.

The one I took out was closed when cold. The gate was not stuck closed but would not hold open with the adjuster until I blasted the thing with carb cleaner.

So far so good.
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PostPosted: Thu May 13, 2021 1:09 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

Never mind what I said about the idle richness afm adjustment. I had the start up then die symptoms again.

The obviously much brighter previous posts were right in at least my case. I put in a spare aav and better.

The one I took out was closed when cold. The gate was not stuck closed but would not hold open with the adjuster until I blasted the thing with carb cleaner.

So far so good.
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PostPosted: Thu May 13, 2021 1:16 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

PuddleRainbow wrote:
Never mind what I said about the idle richness afm adjustment. I had the start up then die symptoms again.

The obviously much brighter previous posts were right in at least my case. I put in a spare aav and better.

The one I took out was closed when cold. The gate was not stuck closed but would not hold open with the adjuster until I blasted the thing with carb cleaner.

So far so good.


Did that fix it or..............?
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PostPosted: Thu May 13, 2021 3:20 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

Lol, sorry for the worst cliffhanger ever....

The carb cleaner rinse seems to allow enough friction for the aav adjustment nut hold the gate open when cold. I can only assume that as the inner workings are a mystery to me. I didn’t put this aav back in the car yet. I have a couple.

The symptoms were that the car would fire right up then die. If not die, the revs would drop so low that the gen light would flicker and double relay would click then recover to a somewhat ok idle. This is when cold.
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PostPosted: Thu May 13, 2021 4:00 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

So, is it working good now or not?

If not, what are the symptoms cold, warm and hot?
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PostPosted: Thu May 13, 2021 4:22 pm    Post subject: Re: 78 FI Super terrible idle when cold. Reply with quote

The guts on those things are fairly simple, a bimetal helix that twists as it warms up turns the disc with the slot in it, the other end is attached to the adjustment nut on the end. It's surrounded by a heating coil.

I'm curious about the symptoms and performance when cold as well, just a lousy idle?, or lack of power and bogging as well?, I'm betting just a bad idle, unlike the AWOL OP's problem.
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