97 N* Shaky idle

[N*Caddy]

Hi guys,
It seems that I got the same idle problem like CaddyNewbie, about 50% or more of the time the idle is rough. I would describe the problem as RPM “drops” with a 3-5 sec. frequencies, sometime (very rarely) continuos drops (the car shakes pretty badly especially if is in gear). The engine doesn’t stall, the drops are just a few tens of RPM. Once I touch the gas pedal is like floating on a cloud. Also, some time I got hesitations on highway speeds when accelerating moderately (gas only premium).
About 20000 Km ago I changed the spark plugs (wiring looks fine) and recently I got the TB cleaned, no codes. I went with the car to my mechanic and guess what: that day the idle was perfect (this Murphy…) so no wonder his conclusion: “there is nothing wrong with the car”.
Oil consumption, less than a quarter every 5000 Km, recently I got low on coolant (no leak detected ), I appreciate that the amount and color of the smoke is normal. I also got that grinding-whistling sound at low speeds when the steering wheel is turned all the way (witch I believe is normal). Everything is perfect except that idle thing.
Aa…, the car is a 97 STS with 128000 Km (~80.000 Miles).

History (since I got-it):
- Air Filter and spark plugs changed (Bosch Platinum +4) at about 106.000 Km;
- Fuel pump changed at about 108.000 Km (brand new OEM);
- Brake pads changed at about 112.000 Km,
- Front right wheel speed sensor changed (at 121.000 Km);
- Never drove more than 5000 Km with the same oil (Valvoline).

Returning to the idle problem, it was always there (coming and going). After changing the spark plugs I had a good idle for a few weeks. As an overall image the idle seems to be somehow better than before changing the spark plugs. Absolutely no difference detected after cleaning the TB (except no more that sticky pedal).

Anyway I guess not to many Toyota and Honda drivers get thumbs up to a traffic light when exactly the same car is stopped on the other line...

[chazglenn3]

The generally agreed upon issue with spark plugs around here is that these cars are far more likely to run correctly with genuine AC-Delco double platinum spark plugs. A few have gotten their cars to run okay on Bosch plugs, but the majority that have tried other brands came back to OEM. Also, even thought the wires "look fine", they may need to be changed, also AC-Delco recommended.

[RDHambrice]

Hello N*Caddy
I had similar problem awhile back. Replacement of plugs AND plug wires solved the problem for me. I also noticed my fuel rails were loose so I tightened those. Runs GREAT now.
Good luck,
RDH

[dp102288]

I second staying with OEM. On this forum, no one had recommended Bosch or any other brand.

[N*Caddy]

A, yeah, good point with those fuel rails, when I bought the car (about one year ago) I did notice that for a mysterious reason the previous owner cut the bracket welded between the fuel lines (right were they go under the beauty cover). But since there is no apparent looseness I did nothing about it.
This is the only “funny” stuff discovered on the car so far.
As for the ignition (hoping that the problem is electrical), I think would start with the wiring.

[Ranger]

My $0.02 is the same as everyone elses. A/C Delco plugs & wires.

[1999STSCresskill]

I am experiencing a very similar situation. I had a rough idle very soon after buying my 1999 STS. I changed the plugs AND wires (oem) and my problem was solved.... for a few weeks. Now the rough idle is back and a bit worse. A friend of mine that used to own a repair shop took a quick look the other day. He said it sounded like one of the spark plugs was damaged and arcing, causing the rough idle. He cautiously suggested that I since I'm not a Pro (like him) I may have cracked one when I was putting them in. Even though there's NO WAY I could have cracked a plug I'll check them out anyway this weekend. If one's cracked I'll tell him it was defective when I bought it!

I'll let you know if it solved my problem.

[dp102288]

^^ Yeah do keep us posted. I am hoping to do plugs & wires in the spring.

[N*Caddy]

Update referring my shaky idle…
Yesterday I just had my car to the shop to change the water pump (yeah, she finally gave up on me at 131000 Km).
When they started the engine to check if everything is ok after the water pumps replacement they discovered that my car was shooting fuel (literally).
It turned out to be a small hose mounted on the fuel lines witch was replaced by the previous owner. Apparently the hose was not fuel use rated and in time got socked with gas like a sponge. Well … I did notice a thin sent of gas while driving (especially lately) but according to my mechanic that smell was coming from the fuel tank. Now I know probably why the fuel rails bracket was cut in the first place.
I was very happy to finally find something wrong on the fuel delivery system, possible cause of all those idle shakes (especially considering the misfires on highway accelerations were more frequent lately). Guess what, looks like the problem is not solved yet because in the 100-km or so driven, since I got the car repaired, I felt the shakes once while waiting on a traffic light. Is true, the car is performing like in her best days before the repair but still. Is true I didn’t have the misfires yet (hope to stay that way) but in just a 100 km is hard to tell.
The good news with the water pump is that I was just planing to do a coolant flush, which would have been money well spent…

Before changing the spark plug wire set I will try to unplug each wire to se if I can determine the bad wire (that in case is just one), but unfortunately I don’t have the place and somehow the time to do that. I tried once the front ones and it seems like piston no 2 was not doing much difference with the plug off (I mean not as much as the other three).

Anyway I will keep you updated…

[dp102288]

^^ Wow at the fuel line!! I would have been scared and pissed off at the same time!

[clarkz71]

Originally Posted by N*Caddy

they discovered that my car was shooting fuel (literally).
It turned out to be a small hose mounted on the fuel lines witch was replaced by the previous owner. Apparently the hose was not fuel use rated and in time got socked with gas like a sponge. Well … I did notice a thin sent of gas while driving (especially lately) but according to my mechanic that smell was coming from the fuel tank. Now I know probably why the fuel rails bracket was cut in the first place.
I was very happy to finally find something wrong on the fuel delivery system, …

Call your local Caddy dealer. That fuel rail was recalled. They will replace it with a stainless steel one for FREE. The recall was for 95-97 Cadillacs.

[N*Caddy]

I just came for a hundred km trip and guess what, shakes are there, misfires are there, maybe not as frequent as before and a little more discrete but still… the good news: no more gas smell.
As for the fuel lines recall on the 96-97 (the way I knew, looks like 95 is to), I assumed that the previous owner got it to GM (I mean is a pretty well known problem). I will have to check with my local dealer if my car had it done ore not because if is free who doesn’t like the price! (Not to mention the safety factor involved).
Anyway thanks’ for the advice clarkz71 is not something to relax about…

[Ranger]

No need to check with the dealer. Just remove the silver beauty cover and have a look at the fuel rails. If they are black plastic, they are OEM. If they are stainless steel, they are the recall replacment rails.

[clarkz71]

He said the original owner replaced a small hose on the rail. He couldn't do that on a stainless rail. Checking with the dealer is just to see if he can get a free rail. I don't know if he can in Canada.

[Ranger]

OH Canada! I think we went through this before and it was only a U.S. recall. I forgot about the fix. Yeah, if that was in place, I am pretty sure it is stil OEM.