Engine misfire cylinders?

I switched the coils, and started getting a different error code. Replaced the coil and it runs great now. Thanks.

After driving for approx. 15-20 minutes engines will miss while climbing long hills and if I attempt to drive up a steep long grade when first starting out the engine will begin to lose power and beging to run rough.

I have 185K miles on a 95 SL2 Saturn. When scanning, I get a 74 code fairly consistanly. At idle when the temp reaches half way on the temp gauge the fan will come on and cool the engine off, however, that is only sometimes, lately the fan wont come on, or I can turn the engine off and let it set a few minutes and turn it back on and the cooling fan may be running from the initial start. The fan seems to be intermittant.
When you get a "engine coolant temp/transaxle temp" soft flag, what does that specifically mean and where is the temp sensor for the transaxle or tranmission lacated when regarding this code. I notice one outboard of the transaxle and another located close to the speedometer cable. There are two engine temp sensors. One is a single wire and one is a two wire. Which one is associated with this code? I know my fan relay could be bad, but it does come on sometimes. Could the temp sensors be causing a problem related to the 74 code? Could I have more than one bug. The car sometimes will miss while driving say 55 or it may miss at idle, but just for a second and then run fine for some time either at idle or with a load. I did find one of the four wires melted through to the shield, so that could be part of the seldome miss fire. This is my wifes car. Initially, I took it to Saturn to get a fan blower motor and talked to the mechanic about this loose clinking noise under the car and when on the rack you could hear it when hitting the catalitic converter. He recommended an after market and then scaned the car and found the 74 code. He recommended as a start to replace the engine temp sensor and transaxle sensor, so I bought the two sensor and connectors with pigtails. I haven't done that yet, all this intermittant overheating and some missing showed it self while driving to a muffler shop and has been happening after the cat was installed. Any information you have would be appreciated.

Thank you,

Jeff

Thank you for your response, I'm waiting to involve my son, so we can work on it together, especially since he will be taking over the car. The sensors are made of some composite. I can see why it would fail with being exposed to a range of temperature. Even metal jacketed RTD's that are installed in a well with heat sink compound fail over time when exposed to varing hot water temps. They last much longer when in a chill water application. The mechanic said he has seen them crack open. I may remove to trans sensor and inspect it and save the other sensor as a spare, since they are the same.

I finanlly replaced the 2 wire temp sensor for both the engine and the trans sensor. In the meantime, I started to replace the wire and plugs, because it had been awhile and one of the wires is burned through to the shielding. I can pull that wire off while its running or any other wire and each plug is firing ok. I'm replacing them anyway because that one might have a problem at a specific frequency or rpm. As I pulled the wires off the plugs, 3 of the ports were full of oil 3" deep above the plugs. I got that cleaned out and tightened down the valve cover screws. The inside ones where a little loose, but not excessive. I cleaned the engine up on the valve cover, block, and transaxle. I ran the car long enough to get it up to temp, so the fan would kick on and cool the motor down. That worked, however it will be running for while and just die. I crank it up and it will run again. When I scan, I get a 33 code for Mas/Map too high. For grins I got a EGR gasket and took the EGR valve off and cleaned it to include the intake and butterfly, knowing these things carbon up, which did not fix the problem. I can clear the code and as the engine runs, it will come back. Sometimes the code is present even before the check engine light comes on. While running at idle, the car may around 800-900 rpm, as it warms up and or during the course of 20 minutes, it may die a couple of times, but is easily cranked up. If I hold the rpm at 2000 steady it will begin to hunt and lug down to 1800 and jump to 2100 and then maybe return to 2000. Is the 33 code a solid code?
The manual gives instructions on how to test the map sensor, so I'll do that. 2 years ago I replace the MAP with a 32 code and it was the EGR. That's why I cleaned it, just to see if it makes a differance. Another thing is that after running the engine for awhile, after shutting it off I can hear an intermittant hissing noise, like a tiny drop of fluid dripping on the engine and cooking off. It's on the back side under the fuel rail and between there and the fire wall. I can't tell where its coming from. The upper hose never really pressurizes when the stat opens up, however it feels hotter on the bottom side of the upper hose. I did find the engine temp sensor cracked, however the trans was OK, replaced it any way. Thanks. Jeff

I tested the MAP sensor, with it off there was 5 vdc supplied and with the connector on, the signal voltage was 1.4 vdc at 1100rpm. With in 5 minutes the engine died. I'm going back out to check it.

Drove the car and my scanner showed the MAP sensor sticking at 4.5 vdc. Brought it home, took it off and cleaned it and blew it out with light air pressure. Reinstalled, after idle at park, reved the engine up and down and would hang up at 4.5 vdc at idle. This sensor is 7 years old and I found my old 9 year old sensor from when I replaced it the 1st time based on the 32 code. Since the EGR had been the real problem, I kept it for a rainy day. Well it seems to be working. If you still have any comments on getting this car in better shape before handing it to my son, I would greatly appreciate it. Thanks again. Jeff

Insalled some new wires and bosch plugs. The electrodes were really wore down on the old plugs. The MAP sensor fixed the 33 code. It seems to have a little bit of a miss, very suddle, but runs good.

At some point, I will take the bosch plugs out and the ngk's in. Don't know if you are still looking at this post. I was considering having the timing chain guides replaced and if you go that far, the chain, nylon gears, and maybe the plunger tensioner and or what ever comes in the timing kit. There is no noise but with now a 187K miles and my son starting to commute 40 miles a day to college, I didn't want any issues with the timing since it is an interferance motor. I don't believe there is any noise coming from under the cover. Would this be a good preventative maintenance measure since he will put an easy 20K on by may next year, putting the car over 200K miles. In addition the rpm seems to delay at a higher rpm before down shifting, like from OD to 3rd or 3rd to 2cnd gear.

I had originally set up maintenance for it this morning. Instead of them installing the timing kit, I asked if they would just check the car out for any red flags. They said, once the guides wear enough to hear chain noise, there would be enough time to install a kit as long as I didn't wait too long. The mechanic said, this was one of the best S models that he has seen. I just need to replace the PCV valve and the serpentine belt. He did recommend changing the coolant temp sensor, because he saw the old wiring. I informed him that I had already changed it and had inspected the connector and wires. The terminals were clean and the wires were not corroded. He told me, I should be good to go.
Thank you for your response again. Oh, the performance switch is in normal. I got rid of a 94 sunbird that had 226,000 on it, that was in good shape, but my son couldn't stand that car, so I hope the SL2 will last awhile, besides it did have the lower milage. On the way to a dealership to buy a new car, I stopped at tire factory store and asked the mechanics if any body was interested in buying my sunbird and got offered $700 for it, the dealer would had only given me $500, so no Craig's list, what a deal. I just got to make this saturn last 75,000 miles. Thank you again.