obscene

Hey guys,
I'm a long time lurker, first time poster. A little introduction: I'm currently and aerospace engineering student and consider myself a weekend mechanic of sorts. I look forward to consuming and contributing to this community. I drive a 1999 RX300 FWD (first gen) with 140,000 miles. I bought it from my grandfather, who is a retired mechanic, for $3000 when it had 100,000 miles on it, and it has been pretty good to me. My grandfather bought it brand new, so I know its complete history.

*I know this is very lengthy, but I feel like I need to explain everything I can so that you understand the situation as best as possible. If you want a quick run-down, I included a short-hand version towards the end of the post.*

• Back story:

I am currently experiencing a very light engine misfire that you can only feel during idle, and when the car is lurching with your foot lighly on the brake. It feels vary close to a vacuum leak. The problem started after I changed a knock sensor, the following is a recount of what I've done so far:

I changed my knock sensor 6 months ago with an after market brand, and big surprise, it broke about 2 weeks ago. I changed the broken knock sensor with a OEM Denso sensor, torqued to spec, and it's working great. However, after the second knock sensor replacement, I started to experience engine problems. My cars CEL is throwing P0300 and P0305. As you all know, cyl 5 is on the back bank, so getting to it was a little time consuming, but I got to it and decided to changed all my spark plugs. After I changed all the plugs, I swaped the coil from cyl 6 (front right), which is known to be working, with the coil pack on cyl 5 (this way I could chage the coil pack faster if it was broken). I reset the codes, and waited for the CEL to come back, and when it did, it threw P0300 P0305. At this point, I suspect a vacuum leak (maybe I forgot a vacuum line somewhere, or I broke one). I bought some carb cleaner and sprayed it over all the vacuum lines and gaskets I could get to, there was no change in engine RPM. I checked all the vacuum lines with a diagram from Mitchell 1 and it all seemed correct. Running out of options, I suspected the lower intake manifold gaskets to have gone bad since I reused them from the knock senor replacement. So I bought a full set of gaskets from Fel-Pro (lower intake, pellum, and throttle body), and replaced all the gaskets. This still did not fix my problem. I finally caved and took my car to a very good mechanic shop ($100/hr) for a diagnosis. They told me the injector on cyl 5 was bad. So I purchased a Denso injector online and changed it, again the problem was still there (shop refunded my money). After all this I ran a compression test and all my cylinders are strong, ~210psi, with the exception of cyl 5, which was at ~70psi. I started to expect a bad exhaust valve since I drove with a bad knock sensor for ~1000 miles (sensor went bad durring a road trip. It is my understanding that a bad knock sensor triggers the computer to run the engine lean, not sure though).

• Current situation:

All this back story leads to were I am now, I am planing on pulling the rear cylinder head to check it for damage and what-not. I was planning on removing the upper and lower intake, headers, coils and plugs, removing/ losening the rear motor mounts, jacking the engine up (to gain better access to the rear cylinder head), and removing the head.

• Short run down for those that don't want to read:

1. Changed bad knock sensor
2. Experienced engine proplems after changing
3. Misfire, P0305 P0300
4. Changed all the plugs and swaped coil pack with Cyl6
5. Codes still P0300 P0305
6. Suspect vacuum leak
7. Checked vacuum lines, all good
8. Changed lower intake, upper intake, and throttle body gaskets
9. Problem still exists
10. Had a professional shop diagnose problem
11. Shop claimed bad injector on cyl 5
12. Changed injector on cyl 5 with OEM Denso
13. Problem still exists (money refunded)
14. Ran compression check
15. All cylinders at ~210 psi, cylinder 5 at ~70psi
16. Suspect valve problem on cylinder 5
17. Planning to pull the rear cylinder head by removing upper and lower intake, removing rear header, loosening/removing rear engine mounts, jacking engine up (better access to back head), pulling the head off, and checking for leaks .etc on cyl 5 valves.

• So Club Lexus, my question(s) to you are the following:

1. Do you have any ideas of what my problems could be?
2. Have you ever removed the rear cylinder head, and if so, how?
3. Any tips or suggestions for me in regards to diagnosing problem?
4. Any tips or suggestions for me in regards to removing of the rear cylinder head?
5. I consider any relevant information to be useful information, so don't hold back!
   

• On a side note: (not related to previous questions)

In the past, I've had trouble finding DIY information on the first gen RX300, so I'm thinking about making a step-by-step, idiot proof, DIY guide with high-res pictures and HD video on how to: (all with accompanying torque specs .etc)

1. Remove the rear cylinder head
2. Change spark plugs & change coil packs
3. Drain coolant/oil & refilling
4. Removing upper and lower intakes & gaskets
5. Removing windshield whipper assembly
6. Changing knock sensors
7. Removing / changing engine mounts
8. Pretty much anything on the way to the cylinder head

Do you guys think the community is big enough / will benefit enough from these guides to be worth putting in the hours to make and edit them into a guide?

Thank you for any and all help, all information is valuable, some more than others.

Lexmex

Welcome to the Club.

1. Are you using the factory service manual or something else to help you out? I've done several DIYs (some among the ones you mentioned and a few done by others), 2,3,6 (I think someone may have done 7).

2. When you last drove the vehicle, what was the vehicle experiencing, were you getting a flashing check engine light, any hesitation?

3. What's the voltage on your battery (I ask this, because a weak battery can also keep a P03XX going)?

4. Yes, I'd likely lean toward something internal given what your compression test showed up. However, when you ran the compression check, was any oil dripped into the cylinder (in this case cylinder 5) to seal up the rings for the purposes of the test?

5. The valve is a likely possibility, since it was only that cylinder (if it were two together I'd look at the gasket).

6. Out of curiosity what oil were you running on this vehicle at the point this started occurring?

obscene

1. I am using the Mitchell 1 DIY guide.

2. The idle was rougher than normal, but someone who doesn't really pay attention to these things would never notice it. When you have you foot likely on the brake pedal, you feel the car lurching forward, it is even worse in reverse. The CEL will flash only at idle and not at speed, however, it does not feel like a normal misfire, if the light didn't flash, you wouldn't know it's happening. For the longest time I thought it was a vacuum leak b/c it feels exactly like one.

3. My friend left the door open, so the battery died (car has been garaged for 2 weeks now). And the complete intake manifold is removed, so I can't really run it to tell you.

4. No, I didn't drip oil into the cylinder, I can rerun the test.

5. That's what I'm leaning towards, I wont know until I pull the head.

6. I was using Mobil 1 5w-30 (I change it every 3000 miles)

I honestly feel that whatever is wrong was caused by something I did, b/c before I changed the knock sensor, it ran fine.

I forgot to mention this before, but the second time I changed the knock sensor, I was in a rush and forgot to drain the coolant before loosening the bolts on the lower intake. A little coolant got into the heads, but I cleaned it up the best I could.

Lexmex

Well, since you have everything about opened, I'm sure will know soon enough. I'm generally not a fan of the Mobil 1 5W30 (there are Mobil products I do like though) due to consumption problems I had running the stuff in Mexico, more a bigger fan of the Castrol Syntec 0W30 (running again now since it's back in stores).

One the flashing CEL, that makes sense since it at high speeds you'd be getting the high air/fuel compared to idle.

With knock sensors, I generally change both (also would do the same thing on A/F sensors for the same thing).

carguy07

Think it could be something as simple as a tight valve that needs re-shimmed? Guys don't talk much about valve adjustments on here, but I have to think it's needed from time to time. Would be a lot easier than pulling the head.

Lexmex

No, we don't talk about them and it's actually something that should be done.

obscene

I'm going to have to take the valve covers off anyway, so ill defiantly take a look.