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Think I fixed BOTH my misfire and random no-start!


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A couple weeks ago I posted on here about my warm-start misfire. I thought I resolved it with a bottle of Marvel Mystery Oil, but it still wasn't right. Tonight I finally gave in, bought a bottle of throttle-body cleaner and MAF cleaner, and rolled up my sleeves! :unsure:

I can't even begin to describe the donkey-show on the back-side of my throttle plate! I took a close look before going nuts with the spray cleaner, and I can only describe it as a vile black tar, that had a moist outer layer, and a rock-hard lower-layer that stuck to every surface on the throttle blade, body, and inner-intake. It took 20 minutes of soak-wipe-brush-soak cycles just to get it off. It almost felt like tar. After using an entire bottle of TB cleaner, and 5 or so shop-rags (that turned totally BLACK with goop), I deemed it clean. Unreal how much tar-goop-crud was in there. :blink:

While I had the mass air-flow sensor out, I cleaned that up as best I could with the MAF cleaner spray. It didn't look bad, but it looked much cleaner than when I started.

While I had the intake bellows/tubes/filter-housing out, I got a clear look at the shift-switch, and realized why I had a random no-start! The heater hose clamp was loose, and it would leak right onto the harness and connector for the gear/neutral switch! The entire switch, harness, and connector was SOAKED in dex-cool. I took some brake cleaner, cleaned it all up, and most importantly, tightened up the hose-clamps. Hopefully that's the end of my random no-start issue! (I realized that the car *would* start if I shifted from park to neutral a few times! Makes perfect sense now!)

I buttoned everything back up, disconnected and re-connected the battery to reset the PCM, and fired her up. I can't even describe how much smoother idle is, how responsive the pedal now feels. It's like driving a different car.

I suppose I on a Friday night I should be at a bar or club or somewhere having fun, but this was the best hour I've spent under the hood in a while! I'll report the results in the next few days to see if I've *really* fixed the misfire for good!

Hope everybody has a safe and great weekend!

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I have always said to really clean the TB it takes about 30 minutes and its a dirty job, I have been using a vice grip to hold it open at the linkage stop.

Its a messy job but worth it, it does run so much better when you do it, the throttle response,


Next time use electrical contact cleaner it evaporates very quickly, brake clean is good but it doesnt evaporate all the time

One other thing be careful spraying stuff in your TB, we saw a tech hydrolock a NS spraying solvent in the TB, it pooled and as soon as he gunned the engine the solvent was sucked into a cylinder and a rod was blown out of the side of the block

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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congrats, When I bought my 96 deville I was getting 10mpg and every time the engine warmed up the check engine light came on for the egr pintle being stuck closed. It took me 1 hour to cleean out the TB, MAF, EGR, and the layer of carbon was unbeelievable. That was a year ago and I drive the car hard, so I recently reinspected the throttle plate and It is still clean, I get 17.4 mpg now


Nice, clean, luxury= fine automobile

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What you saw in there was a combination of crankcase gases from the PCV and exhaust gases from the EGR that settle out when the engine is shut down. Clean it every spring and it will be nothing more than a simple wipe down.

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So far so good! No signs of the mis-fire in the past couple days, and still driving very nicely.

The only thing I have left to fix is the exhaust system. Any time I get on the throttle hard from a stop, there's a violet "hammering" of the exhaust against the bottom of the car. I actually think it's from the section of pipe in front of the cat, hitting against the cross-brace that's right under the floor-pan of the cabin. I've lived with this issue for a year, so clearly it's not pressing. But it's starting to get old!

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Consider that you may be overfilling your crankcase oil. oil should be checked & filled only when the engine is hot. Accidental overfilling just causes the excess oil to get sucked into the PCV to the TB leaving a gummy black tar residue.

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