Slightly Rough Idle and Quite Rough Light Accleration

Ok guys, here's a weird one. My 89 SC will do this whether warm, cold, just started, or driven for 100 miles, and it's gradually gotten slightly worse. EGR is blocked off at the EGR valve, and the vacuum to the valve is stopped as well. No check Engine lights, nor codes.

The Problem:

At idle it will run strong (as in- not try to die or anything) but you can hear a slight *pop* sound in the exhaust every few seconds, and occasionally it sounds like a cyclinder misses, but it's usually just the soft popping.

When lightly accelerating the car will almost buck, feels like it's probably not firing one of the cylinders or something. It will only do this at ALL when the vacuum/boost gauge reads between 20-10 mmHg, never from 10mmHg Vacuum - 11 PSI boost. Also the problem never occurs above 2000 RPM.

I'll be thoroughly checking for vac leaks/ other problems today. any ideas are welcome! thanks all!

Dr Feesh

sp;ark plugs fouled possibly a wire

Same Problem!

You've described the problem I've been having down to the last detail! Wow, well any input you get from this would be great. I've been trying to figure it out for some time now. I haven't tried new plugs and wires yet, but I've replaced the fuel, and air filter plus checked the resistance on the Idle Air Control valve + Engine Coolant Temp sensor and the Throttle Position Sensor, they are all fine. I'm pulling a code that says I have a secondary circuit failure on the fuel pump. Not sure if that has anything to do with it or not. OK, so besides replacing the wires and plugs maybe it could be the coils or the ignition timer thing that regulates the coils? I've checked my Vac tubes, they all seem fine. I'm stumped as well.

Thanks

-B

okay, it's good....in a way....to know that someone else has the same problem WinnipegSC - i thought at once that it might be a spark plug or wire, but it shouldn't be - i changed both about a year ago - which of course doesn't rule them out totally. i dont know what could be fouling the plugs....don't burn enough oil to hurt anything. it's possible that a spot got worn in a wire, but i adjusted the wires several different ways and it didn't help. here's what i checked today: intercooler tube leaks(leaked a very minute amount), DIS, MAFS/throttle body accessories, and half-inspection of the vacuum system. didn't have time to be really thorough. i'm 99.5% sure it's not the DIS, i have a new one in, and replaced it with an even newer extra, so it's fine. (had the original go out this summer) i do have an extra coil pack that i may try, since that's easy to swap out as well. i would have thought a code would pop up if it were messed up though. i'm wondering if it could be an injector/regulator problem. my dad and i put a newer gas tank (and 190lph FP) in it this past spring and i replaced the fuel filter shortly thereafter. it doesn't seem to be running rich....i would guess lean if anything. too lean of a mixture or bad spark delivery are all i can think of right now. this whole "running great when you really get on it" stuff is what's throwing me off. it's something very simple, i know ....... just don't know what!

dr feesh

*a few more facts*

car/engine has 224xxx miles on it, always has 92+ octane fuel, oil changed regularly, and hasn't had headgaskets problems since my ownership nor before to my knowledge. i've owned it for 50xxx miles. gonna rebuild soon, but i want to figure this prob out first hmmmm....it would be neat to see how long original everything would last tho.....

dont worry bad o2 sensors.. or possibly a SLOWLY leaking headgasket will fowl plugs as fast as a couple months. At WOT the sheer p[ressure cleans them enough to send a spark i find.. and the fairly rich WOT conditions prevent to early of knock.. but u maynotice ur lack ing a little bit down lw.. not alot but justa little.. id say pull the plugs.. and look either one is coverd in iol or chipped even from sdpark knock.. and or 2 adjacent cylenders seam slightly worn ou. (leaky head gasket )

im no sure exactly hw to do it.. but if u can check teh volatage of each wire as its fireng the plugs u could narrow down ur problem before teh whole changing plugs thing.. cause the bad one will be reciving ALOT more voltage then the rest in an ATTEMP to fire it(AT WOT u got extra juice maybe thast why after 2K RPM the problem stops itrs got enogh juice to fire a bad plug)



my spellings bad cause im leaning out of my bed to type.. damn im tired

Thanks

headgaskets.....you may be right on that one.....hadn't thought about it yet. well, it's about due for a total rebuild anyways. i'll keep an eye on it. noticed a lil bit ago the pavement beneath the pipes was fairly moist, course that doesn't mean headgaskets are leaking either, but we'll see i suppose! i would think it'd be difficult to start though....with a little bit of water built up in the cylinder and all, but i guess it's hard to tell. i'll just have to pull plugs and take a look. well thanks for the input!

dr feesh

I just pulled some codes today and I'm not sure what they are. I got a 41 and a 91. They are both HEGO related, what is ego/HEGO? Is it somehting to do with the vac for the super charger? It's now making a load high pitch wine and pulling these errors. The error are described below from the book

41 - No EGO/HEGO switching detected, system lean (right side HEGO)

91 - No HEGO switching sensed (left side HEGO)

Does anybody know what these mean?

Thanks

Extra.. Just read up on some stuff.... It's a sensor for the catalyst? O2 sensor? No, I don't think so, Combustion problems.... ?

DrFishbone said:

headgaskets.....you may be right on that one.....hadn't thought about it yet. well, it's about due for a total rebuild anyways. i'll keep an eye on it. noticed a lil bit ago the pavement beneath the pipes was fairly moist, course that doesn't mean headgaskets are leaking either, but we'll see i suppose! i would think it'd be difficult to start though....with a little bit of water built up in the cylinder and all, but i guess it's hard to tell. i'll just have to pull plugs and take a look. well thanks for the input!

dr feesh

Click to expand...

had same prob with 2 of mine. 89sc was the fuel pump. not enough pressure. 93 lx 5.0 head gasket. threw some KW block seal in my 93 and got another 100k miles out of it before i sold it, still running strong.