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Oil pressure drop while at idle?


Blandnuts
09-20-2004, 06:15 PM
Currently my 98 blazer has been dropping low oil pressure while at idle and "studders" when moving from a complete stop. My pcv valve was bottoming out (I could hear it) so I replaced it thinking this was the problem. Well, I have a new pcv vavle and the same problem. With the dummy/stock oil pressure guage it reads about 60 psi while driving. At idle it usually stayed at 40psi but now drops alittle below that and the car will "studder" then it trys to shoot back up to 40 psi.

Could this just be a bad vacuum leak/kinked hose? To my understanding, the car pulls the most vacuum at idle... Anyways, thanks for any help.




fred

Mikado14
09-20-2004, 06:35 PM
If the engine is stuttering, don't worry about the oil pressure. I am assuming that when it stutters, the rpm is low and it is close to stalling out. A vacuum leak will cause this. If you have a vacuum guage check it. You should have about 17 to 19 in/hg. for normal idle. If the vacuum is good and more than likely it is, go and check the IAC, it could be closed off or your throttle body needs a good cleaning.

Blandnuts
09-20-2004, 08:14 PM
Hey, thanks a lot. I'll check that stuff out tomorrow if it stops raining :).



fred

Alexxn 00 Si
09-21-2004, 12:10 PM
Mikado, is cleaning out the thottle body a big deal ? I have a shaky idle too and replaced everything (cap rotor plugs wires air gas pcv) I'd like to try cleaning the throttle body and should I also clean the IAC ? How do I go about doing this ? Might this help ?

Thanks !

Blandnuts
09-21-2004, 01:15 PM
I think my problem is more along the lines of the IAC being bad then the throttle body. A dirty throttle body makes sense as to causing a "little" problem at ideal which might just be your problem. If the IAC is anything like the one on my mustang it's pretty easy to clean...I'll let you know if no one else chims in.



fred

BlazerLT
09-21-2004, 03:11 PM
I think my problem is more along the lines of the IAC being bad then the throttle body. A dirty throttle body makes sense as to causing a "little" problem at ideal which might just be your problem. If the IAC is anything like the one on my mustang it's pretty easy to clean...I'll let you know if no one else chims in.



fred

Befoer you start replacing random sensors and valves go and tune up the truck.

New:

Plugs (NOT BOSCH PLATINUMS!)
Cap & Rotor
Air Filter
Fuel Filter

Do the normal maintanence that you should be doing before you go into replacing other parts.

Blandnuts
09-21-2004, 09:36 PM
All that has already been done, thanks though. I know not to throw parts at a car...just thinking about it reminds me of my auto teacher bitching at us about doing that ;).



fred

BlazerLT
09-21-2004, 09:41 PM
So EVERYTHING on that list has been done?

When were they done. Be more specific.

Blandnuts
09-21-2004, 10:14 PM
All less then 6 months, with the air filter being about 3 months...

BlazerLT
09-21-2004, 10:18 PM
Do you have any check engine lights?

Have you replaced your PCV valve lately?

Blandnuts
09-21-2004, 10:22 PM
No, I don't have a check engine light. PCV valve was replaced 4 or 5 days ago.

BlazerLT
09-21-2004, 10:28 PM
What plugs did you use?

Blandnuts
09-21-2004, 11:00 PM
To be honest I don't remember, but I know they weren't anything platinum.

BlazerLT
09-21-2004, 11:05 PM
I would go to a local mechanic and have the truck hooked up to a scanner and have it's sensors monitored.

If you don't you will just spend triple the money throwing parts at the truck.

Blandnuts
09-21-2004, 11:15 PM
Well, thanks for the help but I'm not throwing any parts at the suv. I've only replaced what has been needed/regular maintenance.

BlazerLT
09-21-2004, 11:33 PM
I was not commenting on your repair practise so please stop taking it as a personal comment against you.

I was commenting on the potential situation.

Mikado14
09-22-2004, 10:03 AM
Cleaning the throttle body is no big deal. Remove the air inlet hose and be sure to disconnect the IAT. We use 2+2 and put a rag under the opening to catch the runnout. Also, spray the butterfly, both open and closed. While wet and with the butterfly open, take a rag and clean the ring of crime and varnish where the throttle body rest at idle, you'll see it. Let the 2+2 evaporate and reassemble.

Remove the IAC, use crocus cloth to clean the plunger. Take a wire bush and lightly clean the seat of any carbon. Clean the seat with crocus cloth and reassemble.

Alexxn 00 Si
09-22-2004, 10:18 AM
Thanks !

BlazerLT
09-22-2004, 11:04 AM
Cleaning the throttle body is no big deal. Remove the air inlet hose and be sure to disconnect the IAT. We use 2+2 and put a rag under the opening to catch the runnout. Also, spray the butterfly, both open and closed. While wet and with the butterfly open, take a rag and clean the ring of crime and varnish where the throttle body rest at idle, you'll see it. Let the 2+2 evaporate and reassemble.

Remove the IAC, use crocus cloth to clean the plunger. Take a wire bush and lightly clean the seat of any carbon. Clean the seat with crocus cloth and reassemble.

I don't recomend using a wire brush for this work and it could be abrasive and damaging.

For the IAC cleaning I did lastnight, I used an old toothbrush soaked in throttle body cleaner and it cleaned it easily.

Carbon is very soft and easily dissolved and doesn't require heavy scrubbing.

Mikado14
09-22-2004, 06:16 PM
The operative word here is "lightly" and further, it was stated to polish the seat with crocus cloth. This is standard practice in some repair manuals.

Blandnuts
10-05-2004, 04:31 PM
If the engine is stuttering, don't worry about the oil pressure. I am assuming that when it stutters, the rpm is low and it is close to stalling out. A vacuum leak will cause this. If you have a vacuum guage check it. You should have about 17 to 19 in/hg. for normal idle. If the vacuum is good and more than likely it is, go and check the IAC, it could be closed off or your throttle body needs a good cleaning.


I checked the vacuum and had 18 in/hg. This was when the car was idled at about 600 rpms (give or take 50 or so). I did clean the IAC and throttle body the best I could while fire ants had their way with me :(. I also replaced some vacuum lines that were old and could cause a possible leak. The problem is still there.

Can I check the voltage coming from the IAC to see if it is within spec? Also what is the voltage suppose to be on the TPS during KOEO? I never adjusted the TPS when I replaced it a year ago.


Thanks
fred

BlazerLT
10-05-2004, 10:17 PM
Any check engine lights?

Blandnuts
10-07-2004, 01:21 PM
Any check engine lights?


Nope.

BlazerLT
10-07-2004, 03:15 PM
Have you done any mods?

Blandnuts
10-07-2004, 09:41 PM
No, this is my daily driver. I have the stang for that ;).

BlazerLT
10-07-2004, 11:56 PM
The oil pressure dropping is just because the engine is coughing when you take off.

I have a feeling the MAF sensor might not be up to par.

Blandnuts
10-08-2004, 12:17 AM
It drops when the car is at idle but never actually feels like it's going to stall (never drops below 500rpms). I would take it to a friend to pull the codes but the engine light has never popped on.

If the MAF is bad, would it cause an increase in air being pulled through the pcv valve?



Fred

BlazerLT
10-08-2004, 12:40 AM
MAF is in your intake hose.

The flicking oil pressure is due to a plugged oil filter going into bypass or the oil pressure sender for the gauge is going bad.

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