High idle, flat spots in acceleration....

[FormulaReed]

The other day, I noticed that I had a a flat spot around 2.5k to 3.8k, it was running fine, but not driving great. A few days later when I went to start the car, it would not idle, like it was stuck at 1.8k or so, even if I blipped the throttle, it stayed high. I turned the car off and when I restarted it, it was like it was running on 6 cylinders. I shut it off and started it again and it ran good. No missing, idling around 800. I drove around the block and it ran ok, but as I coasted to a stop sign, she shut off. It started right back up, but I just went home.

I did the paper clip code read and it gave me a code 22, 33 and 34. I checked the map sensor for a vacuum leak, but did not find one.

I’m thinking about replacing the map sensor and TPS this weekend, but before I do, is there any tips or tricks before I start replacing parts? I’ve read about the hose cracking or coming loose on the map, is there a way to add a hose clamp or something to that like?

Thanks,

Reed

[Ccmano]

What year car is this?
H
:cheers:

[FormulaReed]

It’s a 1991

[Ccmano]

So we can rule out EGR. Sounds like a vacuum leak somewhere in the manifold vacuum system. Before throwing parts at it I would do a through search for vacuum leaks possibly related to the MAP Sensors. Did you look at both MAP Sensors for leaks or hoses off? Check out Haibecks article on the subject. Again sounds like the leak is in the manifold vacuum system not the secondary vacuum system.

http://www.zr1specialist.com/HAT%20Web/articles/Finding%20and%20Fixing%20Vacuum%20Leaks%20on%20the %20LT5%20Engine.pdf

http://www.zr1specialist.com/HAT%20Web/presentations/Finding%20and%20Fixing%20Vacuum%20Leaks%20on%20the %20LT5.pdf

H
:cheers:

[FormulaReed]

I’m thinking that there’s a vacuum leak at the map too. Any tips on finding it?

I’m goin got replace the tps, the throttle response has always been a little off and it’s a cheep part.

[Ccmano]

I’m thinking that there’s a vacuum leak at the map too. Any tips on finding it?

I’m goin got replace the tps, the throttle response has always been a little off and it’s a cheep part.

If you don’t find a leaking vacuum line and suspect the MAP sensor itself swap it out with the other MAP sensor under ECM and see what happens. For the TPS what voltage does it show at rest with Ignition on? Should be .54volts +- .05. You can probe into the connector with a volt meter to get that. Ground the negative voltmeter side anywhere you can find a good ground and probe with the positive side.
H
:cheers:

[A26B]

If you don’t find a leaking vacuum line and suspect the MAP sensor itself swap it out with the other MAP sensor under ECM and see what happens. For the TPS what voltage does it show at rest with Ignition on? Should be .54volts +- .05. You can probe into the connector with a volt meter to get that. Ground the negative voltmeter side anywhere you can find a good ground and probe with the positive side.
H
:cheers:

The look-alike sensor under the ECM is actually the MDP Sensor( Manifold Differential Pressure Sensor). It is different and the harness connector is different so they are not interchangable.

[Ccmano]

The look-alike sensor under the ECM is actually the MDP Sensor( Manifold Differential Pressure Sensor). It is different and the harness connector is different so they are not interchangable.

Interesting I always thought they were the same. I happen to have both sitting on my work bench. At the very least the harness connector is the same between the two as you can see from the photo. They do serve different purposes. Looking them up in the GM parts reference the do show different part numbers 16006834 for the MAP sensor and 16137039 for the MDPS sensor. As always you are correct Jerry! Thanks for the input.
H

http://a65.tinypic.com/2vucw9u.jpg

[A26B]

The harness connectors do look the similar but on a closer look you can see a small tab that aligns with a slot in one of the 3 pins. It's located differently on each sensor.

MAP
https://cdn10.bigcommerce.com/s-nkg90o/products/859/images/2182/12085502__99776.1495485234.120.120.jpg?c=2


MDP
https://cdn10.bigcommerce.com/s-nkg90o/products/877/images/2180/88862231__56482.1495484257.120.120.jpg?c=2

[FormulaReed]

Is there a suitable alternative for the loctite 796 & 416 that Marc Haibeck recommendations? I can’t find it for sale. Pretty sure I’ve got a leak at the map hose and want to seal it.

[FormulaReed]

Just an update to my issue.

I replaced the tps and replaced the map sensor hose with a section of vacuum line. At first the car ran great, but after 3 drives, it was much worse than before. I got a replacement map hose from Jerrys gaskets and once it was in place the car ran great. I learned my lesson about using regular vacuum line, once it got warm it’s just too soft.

I’m putting together an Android tablet scanner so I can properly set the tps voltage, but even the way it is, the car runs better than I’ve ever had it.

[FormulaReed]

Well. I thought I had this issue solved... might have solved this one, but now it’s got a similar problem.

I went for a drive this morning. She started right up, smooth idle ran great. Went to a cars and coffee that was about 20 minute drive from my house. She ran feat the whole what there.

When I left, she started right up and ran good. However about 5 minutes of some stop and go, right about when it warmed up, it started having some throttle surge/flat spots but was still running. But when I pulled up to a stop light she shuttered and died. I cranked it over and it restarted but ran poor. I pulled it over and shut her down.

I checked under the hood to see if the map sensor hose that I just replaced had come off, but it was firmly in place. I gave it a look over and didn’t seen any thing obviously wrong.
I restarted the car and it fired right up and was running fine.

I got most of the way home before the surge/flat spot returned as I was driving up a hill at about 3-3.8 rpm. Didn’t die, but was cutting out. I never got a cel.

I will check the codes later, but any one have any ideas on where to look? Could the map sensor it’s self failed? I’m thinking it’s a sensor of some flavor. Would it toss a code if it’s an intermittent fault?

Thanks,

Reed

[FormulaReed]

I pulled the codes today and I got a code 42.... so I’m kinda freaking out that the ignition control box is going south....

Anything I should check? I’ve heard that the knock sensor can cause this code, is that true? Any other tips?

Cheers,

Reed