I have an '86 and I have noticed that within the past 2 days when I am at a red light{or stopped with the car in drive} it will go from a 600 idle to a 7 or 800.Tonight when I was going home it even dropped to a 500 at one point.It does have a constant rhythm in doing so.The fuel pump and filter have all been re-placed recently.Although the oxygen sensor has not.Also,I am not running the A/C when this happens.What in hell is this??Thanks in advance for any info.

 

What are your IAC counts? if you cant scan The first thing I'd throw at it would be an IAC solnoid.

 

I'm still having the same problem! At idle it was surging from 450 to 850.

Here's what I've done so far...

Vacuum lines, almost all of them. IAC motor, O2 sensor, complete tune-up, cleaned the TB, reset the TPS and the IAC.

All of these things improved the condition slightly. It hunts from 500 to 800 It improves when I turn on the a/c. I'm going to pull the intake tomorrow and replace all of the topside gaskets. If that doesn't fix it I'm just going to raise the idle a smidge...I'm tired of messing with it...I have an older scanner. I will go see if I can get IAC count figures now...brb.


Okay... I have a stored code 32 (egr) I knew this would be there. I'm hoping that's the obvious trouble when I get under the plenum.

Tps volts .56 at 1000 rpm, .54 with the engine off.
Idle Air Pos no AC 040-043, with AC 045-047
Knock retard 002 (wonder why that is?)
Block learn counts 124
Inj pulse width 1.42-1.44
Air flow 011
O2 counts 022-025
Prom ID (stock chip) 7805

There are the numbers...


[Modified by MtlSphere, 1:31 PM 7/26/2003]


[Modified by MtlSphere, 1:50 PM 7/26/2003]

 

Does This car has the stock cam? Your IAC counts are dead on for a stock one. What temp? is the car in closed or open loop? when it happens


[Modified by ASRoff, 9:49 PM 7/27/2003]

 

I'm really not sure about the cam. I'm of a mind that it's not stock. The idle is just a bit choppy but just off idle she pulls for a ton. And the engine shows the signs of having "been into" if you know what I mean; after all it is 18 years old and only God knows what number owner I am.

The ecm was in closed loop and the temp was 205* when I recorded those numbers.

Thanks for your reply!
Make the:seeya

 

I have had the same issue with my 86. I've changed everything you have and maybe a little more. A new IAC didn't change the problem at all. I'm also having problems at WOT. As I reach WOT the car stops accelerating and sounds as if it's missing on a cylider or two. I haven't been able to find the problem either.

Also, I had a code (44 i think) for the knock sensor voltage low a couple of times. Haven't gotten that code in a while though.

:banghead:

 

Hi I think code 44 is the 02 sensor and we also changed the upper air intake sensor whitch helped for awile but is your problem hapen when its hot hot out:cheers:


[Modified by wirenut3, 11:12 PM 7/28/2003]

 

My '85 is hunting too. It goes from 5K to 7.7K to 10K and back and forth. Just been too busy to figure it out. Thinking it's the IAC or a sloppy throttle shaft. It has 172K miles now and I haven't replaced anything on it except the TPS and the EGR temp sensor. Guess it's about time to start taking a closer look. Check engine light comes on and off. Easy to pull the codes, still got to do it. Seems to be a common problem. :(

 

My 85 has done this ever since I bought it with 40,000.I have failed every time trying to fix it with sensors.I even put in a new AIC last night but that did not help ether(but the car runs better now). So I am thinking that its possibly worn Throttle Bodys thats causing everyones car to do this?

 

That was among my first thoughts...worn TB bushings. Calls to local carb shops and vette clinics in town said "no". That the engine is less sensative to throttle shaft play than a carbed engine. I can't vouch for that personally but what I can tell you is that I slathered a great deal of grease around the throttle shaft to temporarily seal any leak at the shaft and came up empty...made no difference to the hunting idle.

So...I'm pulling the intake this weekend. I'll get some new stones and wheels for the dremel so while it's apart and I'll do some gasket matching on the runners and plenum. Hopefully I'll find a leaking egr or something obvious under there. I'll let you know. The valve seals are worn and I get that annoying puff when I start her. I'm thinking of being really ambitious and at least change the valve seals...but man! Wouldn't a cam change feel good?

Something's gonna happen this weekend...just don't know what yet!

 

egr/egr solonoid; first can be checked by vacumn tester and later by test light

 

A worn bushing on the opposite end of the TB shaft from the TPS will cause the TPS to move. The ECM thinks the there is a demand for fuel as relayed from the TPS. It will deliver a burst of fuel raising the idle speed. When the ECM sees o% throttle it shortens the pulse and idle returns to normal. The cycle continues. Just my $.02

 

I wondered about that and used the scanner to monitor TPS voltage while it was idling and surging. The TPS voltage was solid as a rock at .54; no fluctuation at all. But...I've noticed that I'm not getting all of 5 volts at WOT; 4.46 max. For $25 at the Zone I'll shotgun that tomorrow.

Now I've read on the forum that the MAF can cause a "hunting idle" condition without throwing a code...is that possible? If there is something to this? I might have to get one of those test couplers available from MAD to check the voltages with a multimeter. That's not a part I'd like to use the shotgun approach with. :seeya

 

Any progress?

 

Actually, I have made progress. I got side tracked from doing any intake work over the weekend. My AC clutch burned up and I decided to overhaul the ac with a new compressor, orifice tube and accumulator. While I was working with the manifold guages I was sitting on the pass side tire with engine running at 1500. I could hear an exhaust leak. I'd never noticed that before. So I examined the maniflod and found two small cracks at the air tube welds. I JB welded them during the course of charging the ac. After I charged the AC I reset the base idle because I had turned the idle screw up to the aforementioned 1500. When I disconnected the IAC and started it back up I was able to idle it down to 450 in park. I had never ever been able to get it to keep running at that speed before. I use a aftermarket analog tach hooked to the dist when I tune. It wasn't a smooth idle but the needle was fairly stable. Cool enough...I put it drive and set it to 400..still it idled...rough but it was idling and not surging. I shut it down and hooked the IAC back up and then reset the TPS. With the TPS set to .54 volts I can't over 4.0 at WOT so I set it to .58 volts at idle and that gives me 4.15 at WOT (sure would like 5.0 though). Started her up after that and can I just say...smooth? Wow...so I took her for a tester and suddenly she throws a code. I expected as much, code 32 EGR pops up alot. I pulled over and plugged the scanner in and found the code 32 ... but wait...a code 44 too? WTF!...and she started surging again... The O2 sensor is just 3 months old but I might go ahead and replace it again... I cleared the codes and smooth idle again...ses again...surging again...vicious cycle...getting very tired of it!

So, check for exhaust leaks...even tiny leaks won't do! Change your gaskets and see if that helps...

Hey, thanks for asking! :seeya