why the knocking?

howdy! i have a '98 blazer that has 141k miles. recently, when i'm waiting at a light, the engine will "dip" from about 600 rpm down to 400 and then back up real quick. it'll do this every 7-10 seconds until i drive, and then it runs fine. i know i probably need a tune up, but i don't want to shell out $400 if i don't have to. the only other thing i notice is that when the car is idleing, the oil gauge will be down around 20, but when driving, it'll hover at 60. i didn't know if that had something to do with it. thanks in advance for any ideas that could help.

When was the last time you did a tuneup?

I have a 99' Blazer and I am looking at maybe 180 bucks tops for a tuneup. I just did one a couple years ago but bought cheap parts and it's biting me in the ass today.

My Blazer would start puttering like that also here recently. Had trouble towing and taking off from stop signs. Well today I pulled out the cap/rotor and low and behold it looked horrible. So I replaced them only to find out my wires were bad too after such a short time.

So I am just going to put new plugs in while I am at it.

Whatever you do, DO NOT do a half-ass job on a tuneup. Replace it all at once and save yourself the trouble.

i haven't gotten a tune up for it yet. i know when i had my multi-function signal switch done a few months ago, the mechanic said to have a tune up done at around 120k. needless to say i'm a procrastinator. if this is what needs to be done, then i'll schedule one this week.

LOL Then you are just like me. But the end result is something you will be happy with as you won't have to do it again till you probably reach over 200k miles.

I have a 96' S-10 Blazer and I have the SAME EXACT PROBLEM!! Idle= 20psi, or what ever the metric is on the gauge, and at freeways speed it is at 60 psi.

I know i have an oil leak coming form the front of the engine somewhere, I am thinking it maybe the front seal. Just tonight I noticed a bit of a "knock" coming from what looks like the from main pulley (connected possibly to teh crankshaft??).

Anyway, this leak starting, and my sudden oil psi gauge readings, almost coincide or started at the same time.

I think the front seal is integrated with the cover that possibly goes over the timing chain.

My question, sorry to hijack the thread, could this leak cause the big drop in oil psi? Could the now low 20 psi oil pressure somehow caused damage to the timing components and that is why i hear the "knock" right at that front pulley location?

Kramer, are you experiencing any sort of leak in that area??

i noticed that there was a tiny leak of something after we had left it in the garage for 11 days while we were on vacation. this had never happened before. it was dark like oil. my battery meter also varies while i'm driving. not greatly, but it varies. i don't know if that has anything to do with it either.

Every 7-10 seconds means you have the defrost or the AC on and the Air conditioning compressor is kicking on and off.

Might want to go to a service center and have the AC checked and topped up.