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Discussion Starter · #1 ·
Hi Folks -

Was looking for some input from the group on a rough idle on a 78 Spider. After warm-up, the engine seems to have a miss when just idling, not terrible but enough to be annoying. Otherwise, it drives well and pulls strong. I did a compression test and saw the following results...

#1 223 psi
#2 200
#3 224
#4 225

Do you guys think the delta between the #2 and the rest of the cylinders could be responsible responsible for the roughness at idle.

I did spray some starting fluid around the air manifold hoses to see if there's some air leak, but no speed-up of idle.

Thanks for your input
 

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1973 Spider 2L
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I dont think that's your issue. I had my motor running with 180 on the rear 2 cylinders and 110 on the front 2 and it ran as well as you could expect. For a car this old I wouldn't worry about that imbalance. I would check your plugs first. If the spica isn't tuned right you'll see it on the plugs.
 

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Discussion Starter · #3 ·
I thought I had the Spica tuned pretty well, but maybe not. The plugs all look the same, all having a light tan electrode and tip (ignore the sheen on the threads - just some anti seize I put on there). Maybe too lean? I hate to start randomly making adjustments to the FI without having some idea of cause.

The one other thought I have is maybe it's related to the brake booster as it acts up once in a while. Sometimes in the first minute or two of driving, I have no power assist, then it works fine with no issues???

Spark plug Auto part Automotive ignition part Automotive engine part
Gauge Measuring instrument Tool Meter Tachometer
 

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The booster relies off the engine, and boosters rarely go bad. Poor performance=bad or no booster. There's a possibility it could have warn rings, or rings that are starting to wear. When the engine is cold the rings are smaller than what they should be, giving your engine poor compression and causing your booster to malfunction because of a weak vacuum signal. After the engine warms up and the rings have expanded, it corrects itself and gives the proper compression back to make the booster function. Take both cold and warm compression results and compare them, that's where my money's at.

Best of luck.
 

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Discussion Starter · #6 ·
Thanks for the input.

I should have been more complete in my first post. The compression test was done with a fully warmed engine, wide open throttle, and cranked 6-8 turns.

I will do cold check to compare results.

I'm glad to try a different gauge but would like to know the rationale. Should I be questioning the absolute values, or the difference between the number 2 and the rest of the cylinders?
 

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Check the hose from the manifold to the booster. I’ve had them fail from age and lack of attention.

Check little hose from near the idle air adjuster down to the oil air separator.

Most importantly, chech each idle air hose very closely.
 

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The reason that I suggested is a different gauge is the numbers are really high in general. 140 ~ 150 is generally what you expect to see with a stock 2L motor. Has your motor been rebuilt with Borgo 10.4 or Motronic 10.1 pistons? My experience has been that along with the higher compression comes a rougher idle.

You also should look at your ignition timing. If you don't have an electronic ignition now would be a good to consider swapping you old distributor out for a 123 or other electronic distributor.

Another thing you might want to look at is the reference gap on the back of your Spica gap. Remove the long rod and measure the gap between the reference screw and the arm that the long rod attaches to. This gap should be .019" when the engine is up to temp. If that is wider than .019 you need to tune your pump. Get Wes Ingram's book and follow his instructions step by step. Never make a change to the pump that is out of sequence.

Has your pump been rebuilt in the few years? You also want to check your Spica pump to see if it is a leaker. Pull out the dipstick and wipe it on a clean paper towel. Put the paper towel up to your nose and take a good whiff. If you smell raw gas your pump probably needs to be rebuilt. Wes has a waiting list if you need his services.

Get back to us with more information.

- Drew
 

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1984 GTV6, 1973 Berlina, 1987 Milano
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Keep it simple.

I have been tweaking my SPICA Berlina for 10 years trying to get the best performance out of it. I also had a wide and O2 sensor on it until the exhaust rusted out.

Lately I had low oil pressure at hot idle and a rough idle, so I was trying to figure out how to raise the idle speed to boost idle pressure.

I installed a 123 Ignition and advanced it a touch and that helped. But playing with the idle o-ring also helped.

I found that the o ring didn't adjust the idle speed very much if at all. But it does adjust the idle mixture. And if you richen the mixture slightly it will smooth out.

I think you have an occasional lean miss on one cylinder.

What's your idle speed?

Love that color BTW, I miss my fly yellow spider.
 

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Keep it simple.

I have been tweaking my SPICA Berlina for 10 years trying to get the best performance out of it. I also had a wide and O2 sensor on it until the exhaust rusted out.

Lately I had low oil pressure at hot idle and a rough idle, so I was trying to figure out how to raise the idle speed to boost idle pressure.

I installed a 123 Ignition and advanced it a touch and that helped. But playing with the idle o-ring also helped.

I found that the o ring didn't adjust the idle speed very much if at all. But it does adjust the idle mixture. And if you richen the mixture slightly it will smooth out.

I think you have an occasional lean miss on one cylinder.

What's your idle speed?

Love that color BTW, I miss my fly yellow spider.
I was fortunate to buy a very low mile, one owner 115 project. The point being that the components were all largely very close to original.

It required very little time to confirm or correct all of the Spica and ignition adjustments. Yet, I had idle variations and inconsistency. Four fixes have delivered an operation of delightful precision.

A little Tri-flow sprayed down into the distributor advance mechanism.
Replacing a dried and inflexible hose connecting the idle-adjust block with the air-oil separator, along with new spring clamps.
A new idle speed control O-ring. They become inflexible and lose their effectiveness.
Confirming the air intake connection tubes were well fitted and leak free.

Yes, rough idle can be issues with ignition: plugs, cables, cap, rotor, etc. However, tiny air leaks that do not much affect driving speed operations can become apparent at idle.
 
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If your brake booster showed some irregularities I would put a bolt in hose to block off the brake booster and see if smooth idle returns. I’ve had two worn out brake boosters in alfetta an. Oyj caused the idle to crap out. Otherwise I would replace all the vacuum hoses with new, idle oring too. Hoses may look good but they are over 40 years old. It’s worked very well with my Milano and 76 Alfetta. Not to mention 40 year old wiring and connectors.
 

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You can do a cold compression check then put a tablespoon of oil in the cylinder and recheck compression. You should see a 10 to 15 psi difference. The higher the difference the higher the ring wear. I would investigate the brake booster more though. If you have a vaccum leak you'll get a misfire from being lean. A tan plug suggests a lean condition but I'd like to see the tips of the plugs. I'd throw a new set of plugs and block your brake booster and see if that fixes your issue. I like to keep a spare set of plugs for this reason.
 

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Discussion Starter · #14 ·
Thanks for all the great input.

I was able to find another compression gauge that I will use tomorrow as a check of the readings I got using the amazon $40 gauge.

I am the second owner of this car which I purchased back in 1989 with 11,000 miles on it. I don't believe the PO did any sort of work on it in terms of modifying the engine, etc... In '93 I sent the FI pump to Wes to replace the microswitch and do a general check (as an aside, back then Wes received the pump on 9/21 and shipped it back to me on 9/23 - he sure has gotten a whole lot busier since then). The one-page he sent back indicated the pump was in good condition with minimal wear. The car now only has 18,000 miles so hopefully it hasn't deteriorated significantly. At any rate, I don't smell any hint of gas in the oil.

Last year I did replace the points with a cheaper electronic ignition (Pertronix), I tuned the Spica per the John Stewart manual, and put a new TA in it as it was running very rich. Maybe I over leaned it (???). Idle speed varies from 600-800.

When I re-do the compression test tomorrow, I will get a better picture of the plug tips as well as look for potential vacuum leaks (booster, manifold, etc...)
 

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Sounds good. I have found that when setting the mixture I use the digital tac on my timing light rather than doing it by ear. With the engine up to temp have an assistant hold down the gas pedal so you have 3k on the digital tac. Do not trust the tac in the car. Rotate the fuel cutoff solenoid like you would if you were doing it by ear. Watch the tac and stop adjusting when you have the highest rpms on the digital. If you are under or over 3k have your assistant adjust the pressure on the gas pedal so that you are at 3k again. Repeat the process until your peak rpms are 3k. That should be your optimum mixture. As Roadtrip points out, your idle should fall somewhere between 600 and 900 rpms. 750 to 800 is the target. You will get a little fine tuning out of the idle adjustment but not much. Good luck and keep us posted.

- Drew
 

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Yeah... I don't think it should be idling that low, 800 is the minimum for that engine. If I remember correctly it's 800-1000rpm at operating temperature for idle. Also, about the vacuum leaks: I've had vacuum leaks before, and it raised the idle a good few hundred rpm, didn't stutter, become rough, or vary at all.
 

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Discussion Starter · #17 ·
I re-ran the compression test with a different gauge and the numbers were quite a bit lower but still in the 'normal' range. Who knew there'd be that much variability from gauge to gauge. Adding a bit of oil to the cylinders brought the nos. up a bit, but not enough for me to worry about bad rings at this point (see chart).

I did look around for air leaks but did not see any. Most of the air hoses (save brake booster hose) were replaced in the last couple of years.

I will look at the mixture per Spider73's process above tomorrow as soon as I'm able to secure (reluctant) assistance.

1657698
 

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A brick, well placed on the excellerator and wedged under the brake pedal, sometimes does a better job than a reluctant assistant. You can also wedge a screwdriver in the throttle somehow to hold the engine at 3k. I'm not sure how to do that though.

- Drew
 

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Yeah, I'd say that's a little rough. I don't quite recall what the service manual says plugs like that do to the engine, and what causes that, and I don't have the manual with me because it's in my car, which is in my school's shop so I can work on it there. You can also move the throttle body to hold it at 3k if you really needed to, just adjust the screw closer to the firewall. Hope you get it all sorted out.
 
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