...what do they do? I've heard that they don't always set off error codes. I just put a new engine in my car and I'm still sorting it out. The idle fluctuates between 700 and 1100 rpm when warm, eventually it just dies. Seems to run okay besides that. Took it out for a WOT test drive last night and it was running well when all of the sudden it got a sputter and a hesitation accompanied by the Service Engine Light. Limped home and shut it off. Turned out to be a code 33 (MAF). When I started the car back up the hesitation was gone and the car ran great with no codes (idle speed still weird).

Is this a clear cut case?


[Modified by jmr302, 1:33 PM 1/2/2002]

 

I would get the manual for your year and check the MAF relays first. On my 87 there are 2. They are mounted on the firewall near the battery. They are only $10 -$12 each and may be the cause of your problem. The MAF is much more money so hopefully it is not the problem.

Try tapping on the MAF sensor while the car idles, if this effects the idle you may have a bad MAF. Check all the connections.

Look for vacuum leaks they cause many idle problems.

 

Might be the MAF relays also... (a lot cheaper to swap out) when my MAF went in my 86, I got a surging around 50 mph... but the idle was smooth. (did have a harder time starting)

 

Once you get a code 33 then you have to replace stuff, dont wait to see if it comes back, just replace it. First do the two relays on the firewall, i think you can get both for $20 at Mid America. Or i think the local parts stores will have them. Then test it again and if it still dont run right get either a competition MAF (screens on it removed, and its around the same price) or the stock Bosch part.

If your idle is still screwy, check your IAC valve.

 

When I had similar symptoms and code 33 it turned out to be the relay behind the battery - the one closest to the center of the vehicle. There are 2 back there. FYI the current GM replacement has a different picture thing stamped on the housing of the relay. ~Juliet

 

Didn't get any codes when mine went. Would start and then die. Replaced both relays first (was advised to replace both at the same time), but alas, mine was the MAF. Unplugged it and the car would start and run on limp home mode. Something to remember, if you MAF equipped L98 does the above, unplug the MAF first, before throwing a lot of money at ideas and calling the tow truck. :rolleyes:

 

Here is a quote from my 88 factory manual. It is taken very much out of text and may or may not be of value. I offer it because it is easy to do. Also it is under the Code 34, not 33, section.
Page 6E3-A-44: "...low, rough, unstable or incorrect idle problem. If this condition exists, disconnect the MAF sensor. ... If the idle improved with the sensor disconnected, replace it." I repeat this is only a small part of the diagnostics. Hope it helps as MAFs are expensive to replace, and you need to be sure it's bad before you spend the $.
Good luck
Harold

 

O yeah, this may or may not help. http://forums.corvetteforum.com/zerothread?id=205676
I am still suffering this misery.
H

 

Thanks for he input, TPFKATK. I have a feeling that we both have bad MAF's. I have no idea how old mine is. Ditto for the relays. This car is 15 years old now and it's seen plenty of abuse.

I'll try unplugging the MAF tonight as well as tapping the thing while it's running. Didn't feel like running the car last night--it was 7 degrees outside.

Does anyone happen to have the part numbers for the MAF relays? I checked the Advance Autoparts and Autozone homepages and couldn't find a listing for the MAF relays.

 

There is a TSB out on the MAF relays for the early C4's. 86's use two different part numbers while 87's use the same. My local GM dealer had these in stock and they were no more then 20 bucks for the pair.

When you go to replace them, they will look identical.. the relay with the red wire going into it is the MAF power relay. The other is the burn-off relay.

 

UPDATE:

I replaced the MAF power and burnoff relays. There was no change. I also ran the engine and tapped the MAF sensor to see if anything changed. Nothing there. Unplugged the MAF and the idle continued to surge but it was less severe and at a lower idle. The surging occurs when the engine warms up beyond 130 degrees and the idle settles down from 1200 rpm.

Took the car out for a short drive. Drove it pretty aggressively for a couple of miles and everything worked great except for the idle. Finally on the last turn before my street the Service Engine light comes on and the car won't idle at all and has a strange sort of bog/hesitation in the low rpm range. You push the gas pedal and nothing happens for a while and then *ZOOM!* the revs shoot up. Turned the car off, checked for codes, got a 33 and nothing else. Fired the engine back up and the hesitation was gone, no Service Engine light either.

After the drive I noticed that the runner-to-plenum bolts were loose. Tightened them up and there was no change. All the vacuum lines appear to be okay. As far as I can tell the throttlebody-to-MAF bellow is leak free. I wouldn't be surprised if there's a leak somewhere in the TPI intake system. I will have to recheck that stuff. I didn't assemble the thing with any RTV on the gaskets. They didn't look like any was needed. Definitely need some Loctite on those bolts.

I'm running breathers in the valvecovers in place of PCV valves right now. That wouldn't cause a problem would it?

 

sounds like the sensor itself then, i dont know if the breathers would cause a prob or not, i think ive seen them on L98s before though with no problems.