I have a 96 olds 88, with 154,000 miles on it, recently, while the wife was driving it, she went to accel from a stopp light and the engine started running really rough, just prior to this it was running smooth, the upper intake was replaced at 150,000 due to the common failure at the egr port, the engine did have some intermix, but didnot look bad, and the motor did hydro lock, but didnot bend any rods, lucky there, and when new intake was put on, the vehicle started right up and no problems up till now, the check engine lite has been on steady since the intake went out, and code was for a egr sensor mulfunction, could be from the coolant intrusion into it when the intake failed, but it has ran with no problem till now, when the car started to run rough the check engine lite started flashing, i ran the codes last not, and i have p0507, and po300, also had codes for egr again, cleared the codes, and retested, now the only code that comes back is the p0300 random miss fire, does anyone have an idea of where i might start, and what to check first, the vehicle will start and run, at idle it is real rough, and doesnot like to go real good when driving. any thoughts?

P0300 is Random/Multiple cylinder misfire.
p0507 is Idle Control System=Idle Higher than Expected.

Because the top end of the engine was just priorly worked on, the manifold R&R has likely got something to do with your problem. I would go over any wiring in the area with a fine tooth comb. I would also verify that the intake manifold has no vacuum leaks.

thats what i was thinking also, father in law was the one that installed new intake while i was at work, and i know there is a tube that runs inside that manifold that i think is suppose to be part of the map sensor, i do hear like a loud air leak when the car is shutdown after running. could that be the cause of my miss fire? its been running like that since the manifold was replaced and just recently started running really rough. i just installed new vaccum lines to the throttle body as well.

also there is a smell oh like sulphur now while the car is running.

A little bit on the "sulphur smell":



TOC Admin
Brando

the smell only occurs when idling, never while driving. could it be possible that the cat is plugged up due to the internal coolant leak about 4000 miles ago, the vehicle was trying to burn the coolant when the intake went out while i was driving. just wondering

Hi Sirmeza, hello everyone,

Welcome to TOC.


It's still there. You don't smell it because it's blown away by the air under the moving car.


Not yet. Plugged cat would cause a noticable power loss. The cause of the smell was explained in Brandos quote. Driving the car any length of time with a rich or lean mixture is what will cause it to clog, or otherwise malfunction.


Coolant passed through the cat and out the tailpipe in the form of steam.

Regards, Norm

ok i understand that, but that still dont explain the random miss fire code, and why the vehicle is acting like its missing on a cylinder. this vehicle ran for over 4k with the egr valve out, and the intake being replaced with no problems, ran smooth and no loss of power, or fuel mileage, has new plugs and wires, new temp sensor, cause the old one got broken in the process of doing the upper intake, and coils seem like their firing as well, and injectors seem to be too, although i havent tested them yet. the smell just started like in the last 2 weeks, and this was way after the vehicle started running rough.

When the intake was pulled off, maybe its possible that an injector may have not been installed or hooked up correctly, explaining the lean mixture. It may also be possible that the ignition coil, or wires resposible for its operation may have a bad connection, or loose ground. This would explain your misfire... But its definately a theory.

It wasn't intended to.

I believe these guys are better equipped to answer your questions.

Norm

Well, it definately sounds like you have a vacuum leak...has your father-in-law checked it out? Since he installed it, maybe he knows of something he may have forgotten to do....

Was the intake manifold tightened to torque specifications? Is the EGR valve tightened down all the way? Need to check over everything. If you can hear a vacuum leak, open the hood and listen if you can pinpoint where it is coming from.

I was once recommended to use carb spray to find vacuum leaks, spray it over vacuum lines etc with engine running. When you find the leak, you'll notice the idle change as the spray gets sucked up.


TOC Admin
Brando

ok brando, will try that and see, i just got replacing vaccum lines as well. i'll pull that upper intake and check it myself. thanks for help guys, will let know what i find.