Century 3300 Check Engine Light...? help

Hello,

1993 Buick Century 135,000 miles. 3300 V6, sedan.

When I start up the car in the morning the engine starts like normal for three seconds then rpm's rev high and the check engine light comes on. After driving 10 mins the CIL goes off but the idle is still rough and high. The rough idle rough idle feels like a staggering feeling and a misfire a bit but no loss in power and perfect on acceleration/normal high speed. So after hot driving I turn off the car and start it again, the engine runs normal however idle is rough and staggering/hunting still there.

In addition after hot driving, I turn off engine I can smell strong fuel odor coming from tail pipe. Checked for leaks and none. Took to repair shop and they could not find codes but they replaced to new vacuum hoses, fuel injection "flush"and checked for codes..nothing stored in the memory.

Things serviced within 3 weeks:

IAC (Idle Air Control)
Full Tune-up (plugs, wires)
Fuel injection flush
New Fuel Filter
New PCV Valve
Sprayed and cleaned MAF sensor
cleaned intake throttle
New Vacuum hoses

Now, heres the kicker. So I referred to Chilton repair book says sometimes loose wires and frayed wires can cause check engine light to come on due to it not connecting properly. I bought that little packet of some type of wire connecting lubricant that helps make a better connection with terminals so I focused it on emission sensors.

Now when I start it up the morning, no check engine light and no rev high just normal start and rev like other normal cars. The rough idle cold or hot is still there along with the staggering/misfire. The car does not have loss of power or stall. So I take it back to the repair shop and no codes again..

Can it be Oxygen sensor, Throttle Pos. Sensor, MAF...? Im getting frustrated with this situation and any suggestions, same experience are welcome :)

Thank You.

See if there are any stored codes, without that from here we really cannot track this down.

Gotta have some stored codes in there. Wedge, will an IAC set a code on a GM?

If the Check engine light came on, there is a code stored, I don't care what the repair shop said.....

You can check this yourself....this vehicle had flash code diagnostics....jumper "A" to "B" in the ALDL connector....then turn key to "on", (don't start)....code "12" will flash 3x's and then any other codes in the system will flash 3x's....

Can a bad IAC cause a code ? I don't see a code for a high idle....

High idle can be caused by bad IAC, bad wiring, bad sensor to ECM, ECM, vac leak, sticking throttle plate in bore, etc.

As for the 3300 engine, it is probably the worst idling engine, I ever saw GM ever make...customers would come back with a brand new engine and think it had a rough idle....there was nothing wrong...it was the nature of the beast, believe it or not......but while the idle was rough, this son a of gun is a bear on acceleration on the highway....a very sound engine with hardly any problems......If spark output is ok, plugs are ok, injectors are ok, there are no vac leaks, fuel pressure is ok, and compression is ok, this idle is probably ok....

As for your high idle, need to see a scan tool reading of the Idle rpms, and IAC counts....warm engine idle should be around 650 rpms......

When it idles bad, try disconnecting the MAF sensor and see if it runs better....also check the vac line to the fuel pressure regulator for the presence of fuel....

If the Check engine light came on, there is a code stored, I don't care what the repair shop said.....

You can check this yourself....this vehicle had flash code diagnostics....jumper "A" to "B" in the ALDL connector....then turn key to "on", (don't start)....code "12" will flash 3x's and then any other codes in the system will flash 3x's....

Can a bad IAC cause a code ? I don't see a code for a high idle....

High idle can be caused by bad IAC, bad wiring, bad sensor to ECM, ECM, vac leak, sticking throttle plate in bore, etc.

As for the 3300 engine, it is probably the worst idling engine, I ever saw GM ever make...customers would come back with a brand new engine and think it had a rough idle....there was nothing wrong...it was the nature of the beast, believe it or not......but while the idle was rough, this son a of gun is a bear on acceleration on the highway....a very sound engine with hardly any problems......If spark output is ok, plugs are ok, injectors are ok, there are no vac leaks, fuel pressure is ok, and compression is ok, this idle is probably ok....

As for your high idle, need to see a scan tool reading of the Idle rpms, and IAC counts....warm engine idle should be around 650 rpms......

When it idles bad, try disconnecting the MAF sensor and see if it runs better....also check the vac line to the fuel pressure regulator for the presence of fuel....

All excellent info, but I believe a scanner may be required to get a stored code, the link jump may not work.

Thanks guys for responding. I replaced the Idle Air Control about a month ago but it still ran the same. I've been seeing forums and threads that these 3300 engines were made mediocre. They tend to idle rough.. is that true..?

I threw in some Seafoam in the gas tank and noticed my mileage is much better. Its also helping with the engine sounding quieter and not much of a misfire.

Im just trying to save myself from going to dealers and spending too much on something that is pretty common.

Thanks

Max, a '93 should flash codes.....

Yes, the 3300's were famous for a slightly rough idle, that sometimes was thought of as a misfire.....but if you slightly raised the rpms with the accelerator pedal, it was gone....like I said nature of the beast....some people tried to raise the idle, but this caused the engine to jump when putting into gear.....outside of that, it was a pretty good engine...

Max, a '93 should flash codes.....

Yes, the 3300's were famous for a slightly rough idle, that sometimes was thought of as a misfire.....but if you slightly raised the rpms with the accelerator pedal, it was gone....like I said nature of the beast....some people tried to raise the idle, but this caused the engine to jump when putting into gear.....outside of that, it was a pretty good engine...

Correct on all points, but I don't think history codes will flash here.

I have a 92 Buick Century Special and when it rained my engine would ride rough.Found out I had bad spark plug wires had tunup done replaced all wires and spark plugs at 85000 miles fixed that problem.Tuneup cost me $400.00 at midas.Also it is a 3300 engine v6.Recently had check engine light come on constantly.Had mechanic check with his computer for bad sensors.His computer couldn't make connection to car.Told me to replace ECM GOT A REBUILT ECM ALREADY FLASHED from Advance auto for $79.00 mechanic put it in took about 1 hr .I watched him do the whole job change prom etc.So if I have to do it again sometime I am confident I can do it myself.He checked for any codes before hand by jumper had about 6 codes he said codes are suspecious because they are all over the place that is one reason why he said get a new ecm then if he couldn't connect to car he would check for bad wires.Well after he got done installing new ecm started car check engine didn't come on car ran fine and then he checked for bad codes nothing showed up and my car registered on his computer.Also he only chgd me $60.00 for installing ECM.I told him he has my business from now on.