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Discussion Starter #1
After a year I'm finally settled in our new house and ready to put some work into my 164S. The car has a bunch of neglected maintenance that I need to catch up on; my old condo didn't have a garage. Big mistake. For info, it's a US-spec 1993 164S.

Here's my current status: The car has a low, rough idle and what feels like a miss. It fully died while idling in the driveway the other day while I was letting it warm up. On-throttle it felt like there was a miss too so I'm suspecting a fuel delivery or air leak problem, but I'm walking through everything just to be certain. I've done a ton of searching on the forums to get myself started, and here's the work done so far:
  • Compression test showed 174-182 across all cylinders.
  • Checked the cam timing with the paper template. Timing is accurate.
  • Cleaned idle stabilizer (ICV) with carb cleaner, lubricated with WD40. No visual signs of failure or gunk that would prevent function.
  • Adjusted throttle min/max switch position with multimeter. I don't think it was out of range but double-checked it just in case. Multimeter showed good contact and resistance as appropriate when rotating through its range of motion.
  • Tested coolant temperature sensor with ice water and boiling water. All values seemed low compared to what the manual states, but reading the forum it looks like the manual numbers are wrong? Mine showed: 6.07 kohm at 32 degrees (manual states 7.5); 2.705 kohm at 68 degrees (manual states 4.5); 0.214 kohm at 212 degrees (manual states 0.4). I did buy a new sensor anyway (Bosch PN 0280130026) since it's cheap $20 insurance.
  • Checked for air leaks around the intake manifold, plenum, rubber intake boot, intake runners, etc. All hoses pass visual inspection and there was no change in idle speed when sprayed carb cleaner at connectors. I will pull the intake boot from the car to inspect the bottom side for cracks that can't be seen from above.
  • No obvious failure of the fuel pressure regulator - no smell of fuel leaking into the intake.
  • Confirmed throttle cable is not too tight and that throttle valve fully closes at the stop.
  • Checked spark plugs for fouling, they looked good. Replaced plug wires and confirmed condition of distributor cap, no arcing or residue around contacts.
  • I checked the coil for resistance and I think it was fine, but I could have been reading it incorrectly. I didn't see a how-to on the forums.
  • My gauge cluster isn't functional right now (another problem I need to chase down) so I can't check for ECU error codes; can't see the flashing check engine light.
Follow-up questions for the group:
  • I think I read about a possible air leak from a vacuum tank in the left fender? Can anyone confirm? I think I hit all of the other possible air leaks with carb cleaner.
  • How to properly test the fuel pressure regulator?
  • What's the process to test the 02 (lambda) sensor? I've never looked at the exhaust much so I don't know the condition under the car.
  • Proper method for testing the coil resistance?
  • How do I access the ECU, and what's the process for checking that it's properly functional?
  • Thinking about maybe replacing the fuel filter? I doubt it's ever been changed before so maybe it's a good idea to do it?
  • Is there value in looking at the carbon fuel vapor canister behind the intake?
  • Are there any other steps I'm missing that I should go look at?
Thanks in advance! I know this is a lot of questions so I appreciate the discussion.
 

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My suspicions always are that it is the plugs, even if they look good. I'd probably just put in a new set. Use the Iridiums for best long term results.
 

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Discussion Starter #3
Those are the NGK Iridiums, part number IFR6B, right? I'm pretty sure that's what I'm running now, and they appear to come pre-gapped at 0.032 when the manual calls for 0.024-0.028. I know I've never gapped them before so I bet they're out of spec. Even if they're not, maybe a new set is in order.
 

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Iridium plugs last a very long time. In some modern applications they run for 100,000 miles. Yup, basically for the life of the car for many owners. Mind you, if you have one of those I recommend against DIY plug changes!! They get stuck in there.

But, one bad plug can give very poor running and they sometimes do fail prematurely. In old engine designs they tend to foul before the electrodes erode enough to warrant changing. Not sure why.
 

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When my car started stumbling at idle my checklist was almost as long as yours. It happened when the mileage was 66,440, almost 4 years ago, and my notes read: "Got two CELs, one on hot start, one on cold start, cleared fault on ECU with tester. Got more CELs, good idle at cold, now rough idling as car warms up". Plugs and IVC replaced, repaired CTS wiring, cleaned rotor and cap, changed coil. Finally, a (unlit) propane test showed a cracked intake hose (they get hard as a rock after 25+ years), a replacement replica that DiFatta supplied completely solved the problem. As soft as a baby. That hose needs to be pliable as the engine jiggles around a lot, not to mention pulling and pushing every time you accelerate and deaccelerate. Crack was on underside, completely out of sight.
 

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Discussion Starter #7
Pinino, I read a bunch of your thread while I have been troubleshooting, which is exactly why I'm pulling the entire intake boot to visually inspect the underside of it. Any tips on testing the boot while it's off the car? I was thinking maybe taping both ends and blowing some kind of smoke into it? I may have some leftover smoke bombs from the fourth of July, LOL. Incidentally, my motor mounts are shot so I think my engine rocks even more than most! That's another maintenance step I need to take.

I also noticed that I'm missing 3-4 exhaust hangers so I bet I have extra stress pulling on the O2 sensor cables. I have six new hangers I'll be replacing soon, so if anyone has the steps to check that sensor I would appreciate it.
 

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I think the only sure way to test the hose in on the car. The propane test works great and is not dangerous. Keeping the tank upright is recommended, just attach some flexible tubing so you can direct the propane all over, especially underneath, and since the engine will not be flexing at idle, so some flexing and tugging of your own on the air filter cannister, simultaneously directing the propane flow with your other hand. It's doubtful that the cat is moving so much that it would be tugging on the O2 sensor wiring. Remember, all those CTS values are worth nothing if you have a leak somewhere on that hose which causes the ecu to constantly correct.
 

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Discussion Starter #9
Right now the car is a bit disassembled while I was waiting on a new CTS to arrive and for the ICV to get cleaned. I'll have to put it all back together, refill the spilled coolant, and fire it up again to test the boot, hopefully before Friday. You're just using a standard propane torch like this one, correct? https://www.lowes.com/pd/BernzOmatic-Brass-Pencil-Flame-Torch-Kit/1000095816
 

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Exactly. An essential tool for any mechanic and homeowner (my house still has copper plumbing, thus the need for the torch).
 

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I use the Iridiums in all our Alfas, and I have never changed the as delivered gap. They have worked well for years now. My own experience makes me think that plug gap is overemphasized.

Once in a while I go through and loosen and retighten the plugs so that they don't get stuck, although I've never had that happen. It is time to do that with the Iridiums in the 94LS. Hasn't been done in a while since the rear head plugs are more difficult to get to. The NGKs as new do come with an antiseize coating on the threads.
 

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Poor running 164 - I had a thread long ago Dusty Rhodes hard times was the title. 24v but much applies to 12v. Fuel pressure and delivery is first thing. Attach FP gauge and measure pressure - and when turned off too does pressure hold? Then measure glow— beer bottle full in 15 seconds. Next is tramp air - carb or brake cleaner or unlit propane will find the vacuum leak. Last is spark and timing, etc. is your gas old?
 

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Discussion Starter #13
Goats - I'll go read your thread right now, thanks for the heads up. In the meantime I'll go buy/borrow a fuel pressure gauge and run some tests; CarDisc says with the car running, ~45psi at idle w/o fuel pressure regulator vacuum hose connected, then drop to ~38psi when reconnected. How much residual pressure should I see when the car is off? For the flow test, how I can it test fuel delivery with the car off, can I bypass the ignition and run the fuel pump somehow? And finally, yes the gas is old. In my estimate, I haven't put fresh fuel in the tank in about three years or more. Is it possible to "freshen" the fuel with an additive, and if not, is it possible to drain the tank as part of replacing the fuel filter, or do I need to pump it out from the fuel filler as it states in the repair manual?
 

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Discussion Starter #14
Quick update. I watched a YouTube video to be sure I was doing it right, then pulled the coil and put it on the bench to confirm my initial check. I'm seeing 0.6-0.7 ohm on the primary winding (two outside terminals) and 5850 kohm on the secondary winding. The secondary is in range according to the manual, but the primary resistance is outside of the stated 0.45-0.55 ohm range. Is that worth replacing or are those numbers acceptable?
 

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With spark plugs, do not adjust gap on iridium plugs. You can damage the fine electrode. Look at the spark plug box, it will show a picture with an X on a plug and feeler gauge picture (normally). Do not drop the spark plug, you can damage the insulator. Apply cooper grease, or equivalent anti seize (i use grease) to thread of plug, a smear on the thread is enough. This prevents plug seizing in head. Use 8mm (5/16) fuel hose, 6 inch length. Push on plug ,(top), insert plug down plug tube. Hand start and tighten till plug seats using fuel hose. Then torque plug to 25nm. The plug seal/gasket is also an external head gasket. Many people under tighten spark plugs. They can leak minimal compression, and over heat the insulator causing misfire problems in certain conditions. If you follow this procedure, you will not have any issues on your next plug change.
 

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Another quick diagnosis for suspected air intake leaks, get a can of carby cleaner. With a warm motor, idling, give it a quick squirt around hoses and intake manifold gaskets. ANY air leaks is found as the carby cleaner gets drawn in , engine revs will raise and motor will smooth out.
The real correct way, the long forgot mechanics tool, a mechanical vacuum gauge.
 

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How to run fuel pump with motor off is in list of my of Maintenance TS tips:
Fuel pump relay is next to red stripe relay and ignition coil.
 

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"With spark plugs, do not adjust gap on iridium plugs. You can damage the fine electrode."

Really? Then how do you adjust to .025 (Steve Alfisto's recommendation)—just starr at them using the power of suggestion? Of course they can be adjusted, done carefully.
 

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After a year I'm finally settled in our new house and ready to put some work into my 164S. The car has a bunch of neglected maintenance that I need to catch up on; my old condo didn't have a garage. Big mistake. For info, it's a US-spec 1993 164S.

Here's my current status: The car has a low, rough idle and what feels like a miss. It fully died while idling in the driveway the other day while I was letting it warm up. On-throttle it felt like there was a miss too so I'm suspecting a fuel delivery or air leak problem, but I'm walking through everything just to be certain. I've done a ton of searching on the forums to get myself started, and here's the work done so far:
  • Compression test showed 174-182 across all cylinders.
  • Checked the cam timing with the paper template. Timing is accurate.
  • Cleaned idle stabilizer (ICV) with carb cleaner, lubricated with WD40. No visual signs of failure or gunk that would prevent function.
  • Adjusted throttle min/max switch position with multimeter. I don't think it was out of range but double-checked it just in case. Multimeter showed good contact and resistance as appropriate when rotating through its range of motion.
  • Tested coolant temperature sensor with ice water and boiling water. All values seemed low compared to what the manual states, but reading the forum it looks like the manual numbers are wrong? Mine showed: 6.07 kohm at 32 degrees (manual states 7.5); 2.705 kohm at 68 degrees (manual states 4.5); 0.214 kohm at 212 degrees (manual states 0.4). I did buy a new sensor anyway (Bosch PN 0280130026) since it's cheap $20 insurance.
  • Checked for air leaks around the intake manifold, plenum, rubber intake boot, intake runners, etc. All hoses pass visual inspection and there was no change in idle speed when sprayed carb cleaner at connectors. I will pull the intake boot from the car to inspect the bottom side for cracks that can't be seen from above.
  • No obvious failure of the fuel pressure regulator - no smell of fuel leaking into the intake.
  • Confirmed throttle cable is not too tight and that throttle valve fully closes at the stop.
  • Checked spark plugs for fouling, they looked good. Replaced plug wires and confirmed condition of distributor cap, no arcing or residue around contacts.
  • I checked the coil for resistance and I think it was fine, but I could have been reading it incorrectly. I didn't see a how-to on the forums.
  • My gauge cluster isn't functional right now (another problem I need to chase down) so I can't check for ECU error codes; can't see the flashing check engine light.
Follow-up questions for the group:
  • I think I read about a possible air leak from a vacuum tank in the left fender? Can anyone confirm? I think I hit all of the other possible air leaks with carb cleaner.
  • How to properly test the fuel pressure regulator?
  • What's the process to test the 02 (lambda) sensor? I've never looked at the exhaust much so I don't know the condition under the car.
  • Proper method for testing the coil resistance?
  • How do I access the ECU, and what's the process for checking that it's properly functional?
  • Thinking about maybe replacing the fuel filter? I doubt it's ever been changed before so maybe it's a good idea to do it?
  • Is there value in looking at the carbon fuel vapor canister behind the intake?
  • Are there any other steps I'm missing that I should go look at?
Thanks in advance! I know this is a lot of questions so I appreciate the discussion.
NEVER use carb cleaner to check for leaks. Any spark will ignite it. Corona build-up is invisible. Use silicone spray. Yes, at that age, all rubber/plastic vacuum hoses are suspect !!! Micro crack are invisible. Just replace them all. Use silicone hoses where you can and get those nice stainless chamfered hose clamps with formed and not cut gear teeth. All diameters use the 6mm hex head!!! ( check ebay for hose clamps and silicone hoses!)
 
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