Black'69

Hey guys,
Still tracing down my idle problem, the ECM replacment did nothing. So I'm going to replace the coolant sensor and I thought the MAP sensor, but I can't find a part number for the MAP. What did the '89 use for that?

Also where is the coolant sensor located?
Thanks,
Christ

65Z01

Whoa partner, before you throw any more parts at your problem (what is the nature of the idle problem, please) think about getting a scan tool and a copy of "Chevy TPI FI Swapper's, Guide", by John Baechtel (Amazon ~$15).

But to answer your question:
-your '89 has a MAF in the intake path; the MAP sensor came in '90 & '91 on L98s. This is a fairly expensive piece to replace; maybe you can borrow one from a buddy with a 3rd gen F-body.
-the ECM coolant temp sensor is located under the TB in the front of the intake manifold. The sensor in the block below #6 & #8 plugs is for the gauges only.

If your idle problem is mild have you checked out your EGR valve (if it's still in there), a leaking unit gave me idle problems on my '86 IROC though no code 32. There is an EGR diagnostic method on my site.

Black'69

Yeah, throwing parts at it is starting to get expensive. It's starts to surge at idle after it warm up to about 200 deg or so. I'll check the egr now and see if that's the problem.
Thanks,
~C~

Black'69

Quick question, where do I look on the EGR valve to see if it's opening? It just looks like a solid canister?

Steel Blue 91

Could be that you might just need to clean the throttle body and the IAC passage. If it hasn't been done recently, try it before replacing parts.

BTW - The EGR is on the intake manifold, under the plenum.

Black'69

SB'91,
I already cleand the TB and replaced the IAC. Still no luck. I might have to admit defeat and take it to the shop. :-(

Thanks for the tips,
~C~

65Z01

Did you clean the IAC port under the TB before installing the new one?

Under the mushroom top of the EGR is a small vertical cylinder that moves up/down when vacuum is applied/released. Carefully remove the vacuum line from the EGR valve and the FPR vacuum line from the plenum. Attach a length of vacuum tubing between the plenum and the EGR valve and clamp it so no air can flow. Start the engine, remove the clamp and see if the EGR valve moves. If it does, clamp off the vacuum line and see if the EGR maintains position, if not it is leaking and needs to be replaced.

Use the field test mode on my site to see if the ECM is going into closed loop and staying there when surging begins.

Sam Lam

Do the basics when looking for idle problems. Check: timing, spark plug wires, vaccum leaks or loose vac hoses, fuel pressure, set the base idle speed (use Helms manual technique) and resistance of the fuel injectors. Then go and buy the parts you need.

CFI-EFI

Unless there were BIG changes made to the EGR system in 5 years, the valve shouldn't be sent a vacuum signel at idle. Vacuum at the EGR at idle indicates an electrical (EGR solenoid?) problem, but THAT should trigger a code in the ECM. Or it may be that solenoid is leaking and need to be replaced. There could be dirt or carbon between the EGR valve and valve seat, preventing the valve from fully closing. As stated, the EGR should be closed at idle.

Also, for what it is worth, my parts book shows a MAP for 1989. Testing it is simple. As suggested, don't just throw parts at the problem, trouble shoot and fix what is bad.

RACE ON!!!

Black'69

Thanks Guys! I'll keep hacking at it this weekend and see what I find.
~C~

Mike_88Z51

You may need a new parts book. The 89 had an MAF and did not have a MAP sensor. No MAP sensor is shown for the 89 in the 84-91 GM Dealer Parts & Illustration Guide that I have.

CFI-EFI

My mistake. I'm wrong. My book DOES show a MAP for a 1989, but it is for the LT5, ZR1, engine. Technically, it does show a MAP for an '89, but I never would have mentioned it if I'd read the whole listing. I saw, "1989 and MAP", and quit reading.

RACE ON!!!