Author Topic: Pulsing/Erratic Idle Issues  (Read 3206 times)

Offline Jon87V20

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Pulsing/Erratic Idle Issues
« on: September 25, 2019, 08:52:57 PM »
Hi everyone,

I recently put a new long-block 350 in my '87 Chevy Suburban V20. I put everything from the old engine on it except I replaced the factory intake manifold with an Edelbrock TBI Performer, replaced the EGR valve, and replaced the radiator and installed electric fans.

I have about a 1,000 miles on the new engine and I'm having a few issues. We recently road tripped the truck from around central Washington to central Oregon. It ran pretty well for the most part. Not sure what the gearing is on this truck but it's turning about 2,900 rpm at 60 mph.

It threw a DTC 32 several times during the trip. Usually just shutting the truck down and starting it up again would shut the SES light off and it would be fine for another few hours or so.

I should also mention at one point I was running it at WOT getting on the freeway from a rest stop. When I got to 60 mph and got off the throttle, I could feel the engine surging very lightly, barely noticeable. Felt the same as if you were very slightly pressing the accelerator up and down. No codes were thrown while this was happening.

It started having an issue where anytime I start the engine (hot or cold), the idle will pulse between like 1,100 and 600 rpm as shown in this video: https://drive.google.com/open?id=1T7dPn1o8Apy2IAp-i_LMnGrZhp3owGYq It starts to even itself out after a while, or usually giving it a quick rev will straighten it out. Sometimes the pulsing gets rough enough that it feels like it's going to shut down.

I also noticed it wanted to idle around 1,100 rpm even when warmed up.

Later in the trip I had one random occurrence of DTC 33, 32 and 15 for MAP sensor, EGR and CTS respectively. This happened suddenly at a stop light and I had to keep my foot on the throttle to keep it running. Once I pulled over it did shut down. The plastic connector was broken on the CTS from the engine install so I just had the harness sitting on the pins which was working fine before. I bent the pins slightly on the CTS so the harness would fit tighter and when I restarted the engine, it was running fine again and the SES light was back off...

Before the trip, I adjusted the valve lash.

Today I went out and replaced the coolant temperature sensor as well as the vacuum line from the MAP sensor to the vacuum port on the back of the TBI unit. No change.

I warmed it up to full operating temperature and set the baseline idle (transmission in drive) to about 600 rpm.

After starting it up, it's still have the pulsating idle issue and the idle seems to want to be a bit high. The above video was actually taken after all this was done. Also checked for vacuum leaks using some carb cleaner and didn't find any.

What else can I check? This idle problem and the EGR code is getting bothersome.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Online bd

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Re: Pulsing/Erratic Idle Issues
« Reply #1 on: September 25, 2019, 09:14:15 PM »
How did you adjust the idle speed?  What is the measured fuel pressure?  Disconnect the vacuum hose from the EGR valve.  Do the symptoms continue?  Remove the EGR valve from the manifold and flip it upsidedown.  Pinpoint spray some PB Blaster or another penetrating solvent all around the end of the pintle valve inside the raised port of the EGR valve.  Does solvent bleed past the pintle and puddle inside the adjoining chamber?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Jon87V20

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Re: Pulsing/Erratic Idle Issues
« Reply #2 on: September 28, 2019, 07:45:30 PM »
bd,

I adjusted the idle as follows:

Let the engine warm up to full operating temperature
Turned the engine off
I jumped terminals A & B on the ALDL
Turned the key switch to "ON"
Waited about 30 seconds
Turned the key switched to "OFF"
Removed the harness connector from the IAC
Started the engine
Set the RPM to about 650 with transmission in drive using the torx set screw
Turned the engine back off
Removed the negative terminal from the battery for about five minutes, then reattached
Connected the IAC harness
Removed jumper from ALDL
Started engine to test.

Did I do that properly?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Online bd

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Re: Pulsing/Erratic Idle Issues
« Reply #3 on: September 29, 2019, 01:15:39 PM »
There were a few errors in sequence and an error in the baseline idle (minimum air) setting with regard to an automatic transmission (corrections in red)...


I adjusted the idle as follows:

Let the engine warm up to full operating temperature
Turned the engine off
I jumped terminals A & B on the ALDL
Turned the key switch to "ON"
Waited about 30 seconds
Removed the harness connector from the IAC
Turned the key switched to "OFF"
Removed jumper from ALDL

Started the engine
Set the RPM to about 650 550 with transmission in drive using the torx set screw
Turned the engine back off
Removed the negative terminal from the battery for about five minutes, then reattached
Connected the IAC harness
Started engine to test.


However, don't neglect your thread concerning the Loud Ticking from Injectors.  Injector performance can impact the symptoms reported in this thread.  In addition to other suggestions already made, you should determine whether either of the injectors is dribbling fuel with the engine off.

Regarding DTC 32, disconnect the vacuum hose from the EGR to see whether idle quality symptoms clear up.  With the engine running and surging at idle, unplug the MAP sensor electrical connector to see whether there is any improvement in idle quality. 

Did you use sensor safe RTV when swapping the intake and performing other engine work?  How many miles are on the O2 sensor?  What are the IAC counts reported by a scanner?  Have you performed any of the suggestions previously recommended in either thread?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Jon87V20

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Re: Pulsing/Erratic Idle Issues
« Reply #4 on: February 10, 2020, 07:12:23 PM »
bd,

I finally went out and messed with the truck some more today since it's stopped raining for a minute.

I tried unplugging the both the MAP sensor and the EGR vacuum line (one at a time and plugging one in before unplugging the other). The EGR made no difference whatsoever. The MAP sensor seemed to drop the idle about 100 rpm briefly, but then came back up to 1,200 where it always wants to run.

I did notice if I unplugged the connector under the brake booster for setting the base timing the idle comes down to about 900 rpm in park with the timing at 0°. When the connector is plugged in, the timing is all the up towards the last notch (15° or 20°?). Can't see the numbers on the pointer very well.

Yes. I did use sensor safe RTV when assembling the manifold etc.

The amount of miles on the O2 sensor is unknown. It's been in there since I've owned the truck and I bought it around 2014. It's been driven quite a bit since then.

I don't have a scanner to check the IAC.

The EGR is new (was replaced when the long block went in).

I don't have a fuel pressure tester. What is one that will fit? It was a bit tough to get the fuel lines to mate up with the TBI with the new intake manifold since it's a bit different. I've never used a fuel pressure tester before and I'm not sure how I would fit one in there.

Thanks!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

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Re: Pulsing/Erratic Idle Issues
« Reply #5 on: February 11, 2020, 10:05:50 PM »
I did notice if I unplugged the connector under the brake booster for setting the base timing the idle comes down to about 900 rpm in park with the timing at 0°. When the connector is plugged in, the timing is all the up towards the last notch (15° or 20°?). Can't see the numbers on the pointer very well.

^^^^ This is normal.


I tried unplugging both the MAP sensor and the EGR vacuum line....  The MAP sensor seemed to drop the idle about 100 rpm briefly, but then came back up to 1,200 where it always wants to run.

I don't have a scanner to check the IAC.

When working on electronic fuel injection you need to beg, steal or borrow one.  Perhaps a friend has one or you could "rent" a scanner from a local parts house.  Anymore, OBD 1 scanners are not terribly expensive and they provide a huge boost to diagnostic prowess with just a little practice.  You really need to retrieve codes, monitor voltages and system parameters in real time.  So procure a scanner that has those capabilities.  A decent DVOM is also a plus.


I don't have a fuel pressure tester. What is one that will fit? It was a bit tough to get the fuel lines to mate up with the TBI with the new intake manifold since it's a bit different. I've never used a fuel pressure tester before and I'm not sure how I would fit one in there.

^^^^ This is another basic must-have tool when working on TBI.  Fuel pressure is fundamental to proper TBI function.  Ideally, the gauge should read ~0-25 PSI so that the pressure readings will deflect the needle to mid-scale where the gauge is most accurate.  The greater the full-scale maximum of the gauge beyond ~25 PSI, the lower the resolution.  Unfortunately, unless you piece a test gauge together it will be difficult to find fuel pressure gauge sets under 100 PSI full-scale reading. 

There are two locations to measure fuel pressure: at the fuel inlet to the throttle body and at the fuel filter.  Measuring pressure at the throttle body requires unbolting the steel fuel line retaining clamp from the back of the right cylinder head - a PITA at minimum.  The easiest location to connect the gauge is at the fuel filter inside the right frame rail.  There are variously configured adaptors to accomplish this.  The OEM fuel filter fittings are M16 x 1.5 thread, tube and o-ring.  So any adaptor you use will require that size and style of fitting.

A decent compromise if you don't mind the lower resolution of a 0-100 PSI gauge is the Harbor Freight 64939, Maddox Basic Fuel Injection Service Kit.  The TBI adaptor is imaged below.

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Jon87V20

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Re: Pulsing/Erratic Idle Issues
« Reply #6 on: June 14, 2020, 11:48:44 AM »
BD, once again sorry it's taken so long to update this. I do appreciate the help. I'll be picking up this fuel injection testing kit you linked from Harbor Freight in a few days. I might go out today and test the injectors as you mentioned in the other thread to see if they're dripping with the engine off while priming the fuel pump.

Regarding the OBD 1 scanner, do you have any recommendations on the best place to get one? Does this just plug straight into the diagnostic port under the dash?

Thanks again.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Online bd

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Re: Pulsing/Erratic Idle Issues
« Reply #7 on: June 15, 2020, 09:23:44 PM »
Scanners plug into the ALDL connector beneath the driver side dash. 

Many options exist for OBD 1 scanners with a broad range of pricing: Fuel line size for TBI / Runs rough / Stalls.  Foxwell is yet another brand.  Avoid Harbor Freight since the Zurich brand requires an annual subscription. 
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Jon87V20

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Re: Pulsing/Erratic Idle Issues
« Reply #8 on: June 17, 2020, 01:12:12 PM »
That Bosch scanner looks good. I'll have to wait till next paycheck to pick one of those up, but I did order the fuel pressure testing kit.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline Jon87V20

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Re: Pulsing/Erratic Idle Issues
« Reply #9 on: June 28, 2020, 11:54:14 AM »
Well I got the fuel pressure tester kit. I had a heck of a time trying to attach it though. If I go down by the fuel filter, I can't move the lines enough to fit the tester in. I tried unfastening all the holders but there's one in the frame rail that's blocked by the exhaust. I didn't want to drop the exhaust to get to it. Trying to attach the tester directly to the TBI unit wasn't possible either as the metal lines couldn't move enough to make it fit.

Should I try and find a flexible line that would run from the lines right behind the bell-housing up to the TBI?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Online bd

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Re: Pulsing/Erratic Idle Issues
« Reply #10 on: June 28, 2020, 10:46:16 PM »
You shouldn't need to disconnect the exhaust unless the exhaust was reconfigured by someone.  Unclamping the lines and filter from the frame rail should provide more than enough room to fit the adapter in place.  An alternate style adaptor temporarily substitutes for the fuel filter during the pressure test.

« Last Edit: June 28, 2020, 10:51:26 PM by bd »
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Jon87V20

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Re: Pulsing/Erratic Idle Issues
« Reply #11 on: July 02, 2020, 11:01:35 AM »
Yeah I had grabbed some dual exhaust of a Suburban in the scrapyard. The passenger side piping gets really close to the frame rail. I wrapped the pipe, but I should probably move the fuel lines further away from the exhaust. It's been okay for around four years but it would probably be a good idea for safety anyway.

I'm going to be replacing all the exhaust soon. Maybe I'll run the pressure test when I have it out of the way.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208