I am new to the forum but I have read and used some of the info. posted. My car which is a 1991 Cadillac Devile 4.9 V8. Last month the car started to vibrate roughly. It had a barely noticeable vibrateion maybe (miss) since I had the car now 3 months.
Error code E30 E91, E98 there were others before I reset the codes now these seem to be left over.
What was done: Changed all spark plugs and wires, changed PCV, fuel filter, air filter. Note: some of the spark plugs had carbon and tech person said maybe too rich fuel (gas) or possible coolant leak not confirmed.
Problem: I am trying to fix the (missfire, inconsistent idle)
Question what would be the most likely cause of this problem, I was thinking the EGR valve because when inspected I saw a crack in the base of the part that attaches to the engine. On the forum coil(s) were mentioned as a probable cause please advise steps.

Phut7

 

most likely ...
coils, plugs, plug wires, throttle intake ...


"Error code E30 E91, E98 there were others before I reset the codes now these seem to be left over. " what do you mean by "left over" ?




.

 

Thank you for reading post. The coed that I had before I did anything was E30, E55, E71,E98,E99
F11, F40, F48 (i still do have these F codes which I believe are related to air condit)

To answer question this is what I have presently E30,91,98, F11, F40, F48

 

have you had the tps cleaned lately? also, advise stomper gave...plugs/wires is where id start...

rickyd

 

TPS- I think this means throttel position sensor. Sorry I am still learning. Please let me knwo where it is located and how to clean.

 

tps is at the intake and works the throttle plate.... youll need to take apart. sorry the tps is electrical, and you cant clean it, but you'll need to spray carb cleaner into the throttle plate to clean it ..... spray, rev engine, spray again, rev and spray again. but i would change plugs and wires also. .........big time
rickyd

 

I will try clean up the throttle plate. I mentioned in my original post that I replaced all of the wires and spark plugs about 2 weeks ago. the car ran a little better but the misfire was still happening .

 

yea... i read it and .....well sorry..... brain fart!!... yea clean that plate real good, lets see what happens. also i think at this point i would read in the faq section, WOT... and do that. give'r a good runnin that way, and a good clean..
let the forum know how you make out
rickyd

 

I played mechanic this weekend and took off the TPS to view and "clean" the throttle body fo rthe second time even though it was pretty clean already. Note: when I tried to unscrew TPS both screws broke off. I drilled out one of the remaining screws and palced another screw in its palce.
I have already changed the coil on top of the distributor cap (junkyard to see if changed), rotor wires, spark plugs, fuel filter, air filter, cleaned throttle plate.
Yesterday I took for a drive, still the miss was there but I noticed that the power increased and seemed to accelerate quicker. today I drove it to work and it seems a little better but miss is still there. Any advice?

 

Update- After changing the EGR valve that had a crack in the right base where the screw is located with a (cleaned) EGR valve from junkyard the car improved about 40% (more power, less chugging when up an a hill or accellerating). However I still have what seems to be a miss- ERROR code E30, 52, E91, E98, please advise.