Hello Dan, I was just going through the forum to see if I can find out why my 93 Bonneville has developed a "cough". She has 175,000 miles, new plugs and wires @ 158,000; air filter, fuel filter, pcv changed at 152,000. Two days ago out of nowhere she just started idling rough when stopped and in gear. RPMs go down to under 1,000 and she threatens to stall, but has not stalled yet. In park the idle seems to stay up around 1,000, but it seems it'* still a little rough (perhaps I'm just imagining this part), but once I put it into drive with the brake depressed the idle turns to doo doo. Any suggestions on where I should start looking?

I moved this to it'* own thread.

Could be a number of things. Old spark plugs, dirty fuel injectors, dirty throttle body, vacuum leak. Do you have a check engine light?

Hi Dan, Thanks for your response.

For some unknown reason my ISP can not open the gmforum anymore. It occured when I tried to reply to your reply the other day. Luckily one of my neighbors has an unsecure wi fi so I am on it now to respond.

I have a service engine soon light, however it is not illuminated.

The plugs and wires were replaced about 20k miles ago.

I replaced the throttle body gasket (with your step by step guidance) about a year ago so the throttle body was totally cleaned then.

Since your reply I put in a new fuel filter and air filter and a can of fuel injector cleaner.

The engine seems a little better at idle. When accelerating, at about 45 mph I get the hesitation/misfire?, but if I ease off the acelerator slightly, it smooths out right away and speed will increase. It will then start doing it again as I accelerate to 55mph. Easing off the accelerator smooths it out again. This pattern continues, and I had it up to 85 mph before just backing down to normal highway speed. After running the car for a while, especially at highway speed, when I come back to a stop and the engine is idling in gear, the idle is smooth for a while, but then if stopped for a while at a light it'll start getting rough, the ignition system seems to try to compensate and the idle picks up a bit and will smooth out. But it seems to hunt within itself.

It'* feeling like a fuel problem to me. I guess the next step would be the injectors. Is there a procedure to locate a faulty injector or do I have to just replace all six? Also a step by step on replacing the injectors would be greatly appreciated.

Regards, Rudy

I would look over the coils, I suspect a bad spark is the problem, not injectors.

Ok, a check of the coils I will do, as soon as you tell me how. lol. Is there some sort of test on the coils I can perform with a multimeter?

Rudy

https://www.gmforum.com/trouble-shooting-test-procedures-141/testing-coils-spark-plug-wires-278818/

Hello Dan and JWFirebird,

Wow, Ive been having terrible problems accessing this forum. I've contacted my ISP (Comcast) to no avail. I downloaded Google Chrome and used it today instead of Internet Explorer, and I got through today, but I tried it before a few days ago and couldn't get through with it either. Nevertheless, I'm here today.

I want to thank JWFirebird for sending me the link that Dan laid out for testing my coils. Not only did the procedure work like a charm, after replacing one of the three coils (showed an open on the secondary) my idle/misfire problem is now gone. You hit it right on the head again Dan, probably with that big hammer you have in your file picture. You da man!

I have another question for you. Over the years my oil pressure has dropped little by little in my 1993 Bonneville. I have always used the recommended 10W-30. Now that I have 175k miles on the engine and I see that my oil pressure is a max. of 40 psi at highway speed, and after warmed up at idle can go down to just above the red mark on the console gauge. I was considering switching to 10W-40. I live in south Florida, so its always hot so I figure that the increase in viscosity would help raise the oil pressure slightly, yet with the hot climate still provide adequate flow for full protection. What is your opinion of going to the 10W-40?

Regards,
Rudy

glad we were able to help. The easy fixes are the best.

Generally I say use the recommended oil only. But having a high mileage engine the little bit thicker oil may help. However, when you see the pressure that low, do you notice anything odd with the engine? Odd sounds, etc. There is the chance the oil pressure sender unit is bad.

No, she runs smooth (now, thanx again). There has not been any rapid drop in pressure, this has been cummulative over the 18 wonderful years Bonnie has given me. Just thought she may be in need of a little "Geritol" or if you're too young to know what Geritol was, howabout "Activia or Ensure). I could probably go with the 10W-30 for thousands more before I really need to do something, but I figure what the Heck, we have ways on how to give her a little shot in the arm.

Sounds like I'm gonna give it a try, already have the oil, will change out tomorrow. I will cetainly monitor the gauge (I realize that accuracy in an 18 year old gauge needs to be considered, but it'* all I got and it has never acted erratic), and if I see anything that concerns me I'll be-a-calling, or better said, posting. Certainly there aren't any immediate harmful effects, after all, it is oil, just slightly thicker.

Thanx again Dan
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Rudy