Shudder at startup

Welcome to 2CarPros.

That's a tough one. First, have you checked for an injector leak that could be causing a problem? Also, have you checked for any dirt or issues with the crankshaft or camshaft position sensor?

I would start by checking fuel pressure and a leak down test to see if one of the injectors is leaking. Also, and you may have already done this, check for engine vacuum leaks. If you have a live data scanner, check the engine coolant temperature sensor reading to make sure it is accurate.

Let me know how long the problem lasts and if it goes away by itself at idle. If you could make a video of what it's doing and upload it, that may help.

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Let me know.

Joe

Welcome back:

A plugged heater core won't cause the engine to run hot. Do me a favor. Take a timing light and check ignition timing. Here is where it should be. If it's off, that could cause it to run hot. Here are the specs for timing:

Ignition Timing (After warm up, at idle)

BTDC. 12 Degrees ± 5 Degrees

As far as the running hot, make sure the t-stat is good, the radiator isn't plugged and so on.

Let me know about the timing.

Joe