Problems with 97 tahoe

[Greñas]

I have a stock 97 tahoe 5.7l 4x4 with 127000 miles.
I am experiencing two problem with my tahoe. i think they are separate but I'm not sure. There are 2 codes that are coming up p0305 (cylinder 5 misfire) and p0507 (idle control system RPM higher than expected). Also the O2 sensor (bank one 1 sensor 1) code came up. My thought was that the misfire caused this because when i cleared it, it did not come back but the misfire did.
I will start with the misfire. It is not that noticeable, it is just a little ruff when idling. I replaced the distributor, wires, and plugs but the code came back after a few days. When I first pulled the spark plug i thought that there was more to the problem then just a tune up. As you can see in the pics there is a lot of ash deposits. I did a compression test and it was fine, i dont remember the exact number but they were all pretty close. I then did a leak down test and it was also fine, 1/2 psi difference at 70 psi and less then 2 psi at 90 psi. So my next thought is injectors but would they do this to the spark plug? Any thoughts or ideals would be greatly appreciated.

My next problem I think has to do with the p0507 code. I replaced the idle air control valve and the TPS, it did not solve the problem. But it did help one of the problems, i noticed that my rpms were higher then normal at freeway speeds about 5 to 8 hundred rpms higher. But it did not solve the main problem and that is, when im driving and I take my foot off the gas the rpms drop but my speed does not. It gradually slows down but not any thing like it should. Its like I'm driving in cruse control but the cruse control cable is disconnected and my cruse control has not work for a while. I know that on the ford ranger when the separator plate gasket in the automatic transmission goes out it causes the same problem. I could not find any thing like this happening in a 4L60E transmission. Also when driving at idle the rpms and speed creep up. I can some times get it to go back down if I tap the gas fast. Could it just be the harness to the idle air control valve or tps? Any thoughts or ideas would be greatly appreciated?
Thank you,

 

[SunlitComet]

for that cylinder there is a possibility for coolant seepage into #5. but if your collant has remained unchanged the whole time i would look into a possible worn valve seal especially if it is oil coated. if not oily but thinnish fluid the your intake gasket has sprung a leak. as for the p0507 what usually causes this is a stuck iac valve, the stop screw on throttle body has been adjusted since tb has been built originally or the throttle linkage, shaft or blade is jamming. now the code could also be caused by vacuum leaks or lea/rich conditions.

examine the plugs for signs of specific fluids. get it on white paper somehow as it is easier to distinguish. clean the plug and reinstall. it was new and in for only a few days you said? make a note of fluid levels while cold. while running spray some starter a little fluid on the lower manifold to cylinder head right between the 3 and 4 bolts of the plenum mounting hardware starting from the front on the left side of engine. listen for speed changes. if your cruise has not been working and your rpm have been much higher (it sounds as if your torque converter may not be locking up) then it is possible the brake switch has malfunctioned which can take out both of those as well as brake lights in any combination. any reason to not have that cruise cable connected? are you positive you get the overdrive gear? when you said distributor did that include the cap too? follow this info and it will help narrow the causes and sort them out more effectively.

 

[Greñas]

Thank you for the fast and detailed response.

The previous pictures are of the spark plugs that were installed for 2+ years. I posted some more pictures of the new spark plugs that have only been in for a few weeks. It defiantly looks like oil. If you look at the pictures there is this black sludge on only half of the ceramic insulator. Is this from the oil running down the cylinder walls? Also how come I did not have more of a leak when I did the leak down test?

As for the iac valve I already replaced it but my local dealer did not have it in stock so I had to buy the "best" one they had at O'Reillys. I also found a crack in the vacuum line elbow coming from the pcv. So I replaced the elbow and the pcv but it did not help. I noticed that the grommet does not seem very tight. There is not any slop but it does not seem very tight. How tight should it be?

The rpms when driving are back to normal, they are high when driving at idle. I replaced the distributor cap not the whole distributor. The cruise control cable is not connected because the cable is stiff and does not move. When I reconnect it, it just comes back off.

 

[SunlitComet]

can you guess at compression test number like 140's 150's. just ballpark it. that helps as a reference point. lets assume you have good numbers right now and you have no cylinder wall damage. the only two things that can oil foul just one plug is a bad oil control ring on the piston or a worn valve seal. lets stick with the valve seal for now. a valve seal does not leak thru like a dirty or damaged valve can. the spec clearances in the service manual between the valve guide and valve stem are like 0.001 to 0.0037 in an engine that has been in service for 100k miles or so. not a lot of room for air to leak fast but it still can and might be unnoticeable very easily.

to change the stem seal with out removing the cylinder head involves putting that cylinder at tdc of firing. you would use an adapter that you hook running air to and put it in place of the spark plug so the air pressure is constantly pushing the valves close sorta. while it is on you would remove the rocker arm and valve spring parts and stuff. extract the seal and use a tool that will push the new one down evenly with some light hammering and can fit over the valve stem and the same time. you would do this for each valve on that cylinder. another thing to inspect for valve binding that might indicate a need for some machining work. find wire or rubber bands to fit tightly in the keeper grooves so the valve does not fall in where you can not pull it out and while holding it shut off the air and twist the valve in your fingers while going up and down. if it binds up the clearance should be machined to 0.002. if all is well put the air back on and pull the valve up and it should stay there. proceed with the steam seal replacement and put it all back together and readjust those two valves. or all if you have not done so in tens of thousands of miles. does not hurt when you do it right.

or you could let a shop do all this. if you want to do on your own let me know i can print out the procedure and recommend a part for you.

after a while the valve cover grommets give you loose fitting hoses. you can get new ones gm 10088126. about $8 dollars each and get one for each valve cover. buggers should be real tight fitting then.

for the iac valve lets try resetting it to see if that helps at all.

1. Start the engine for 20 seconds .
2. Turn OFF the ignition for 10 seconds .
3. Start the engine.
4. Check for the proper idle speed.

otherwise lets leave it alone for now.

if you want to disconnect the cruise cable of throttle and control module and see if the cable binds when you move it. if so a new gm 15734164 can be had for about $25.

 

[Greñas]

Sorry for the late reply. I now have some time off of work so I can finally get in to this project.
I do remember the compression for number five, it was 145. I found it on a piece of paper but I did not write all of the other numbers down because they were all close.
I would greatly appreciate it if you could post a print out of the procedures and a list of the recommended parts. Before you said that there is a possibility that it could be a coolant leak. I did have a coolant leak from the heater control valve I replaced it and the hoses going to the heater core. But there is still a small leak. I need to check the hoses for any leaks. I do not see any in my oil. I dont think it is but how would I fix it if it was going in to cylinder 5?
I tried to reset the iac but there was no change. I know you said to leave it alone for now but should I check for vacuumed leaks? Any where in particular?
Also I have an oil pan leak. At least that's what a shop said when I had some shocks put on. I'm hoping that it is that and not the rear main seal. It is 4x4 and some people said that they had to jack the motor up some said they did not. Any information on this would be appreciated.

 

[SunlitComet]

for now just try snugging the oil pan bolt a bit in case they have loosened. and yes with a 4x4 doing the oil pan gasket can get cumbersome. thought you did check for vacuum leaks already. check around where the manifold mates to the heads and around the various vapor/vacuum hoses.

 

[Greñas]

I sprayed some starter fluid around the mentioned areas and did not notice and sound or rpm increase. I have a Bluetooth obd reader that's paired with my phone so I was monitoring rpms when spraying starter fluid and did not see any increase. I posted some screen shots of the real time info. The first one is in park at idle. The second one is in gear at idle. Are the rpms while in gear too low? Also is there any thing that I would be able to tell from the vacuume readings? I can also graph the readings if that would help. So I could compare speed and rpms or vacuume or any combination of 2 readings.